Although personality tests are accurate and reliable in assessing the personality of subjects, scientists studying the relationship between blood type and personality through personality tests often reach different conclusions.In 1964, Cattell et al [6] administered the 16PF High School Student 16PF to a total of 581 adolescents of Italian descent aged 11 to 18 years in four cities, including Rome, Florence, and Palermo, Italy, and Boston, USA The test was used to analyze the relationship between blood type and personality in these populations. The results showed that adolescents with different blood types performed similarly on all dimensions of the 16PF, but that adolescents with blood type A scored higher on the I: Sensitivity dimension. That is, adolescents with blood type A were more sensitive, emotional and empathetic than those with blood types B, O or AB. Other studies based on the 16PF [7] have since shown that type A is more self-indulgent than types B and O, and that type A is more anxious than type O. Type B, on the other hand, is more emotionally unstable, has a greater sense of apprehension, and is more easily stressed, i.e., Type Bs are more emotional. Other studies based on the Eysenck Personality Test (EPQ) have yielded inconsistent results. According to one of the designers of the EPQ, H. J. Eysenck himself [8], a higher percentage of introverts were type AB, while type A was more emotionally stable than type B. Lester has since compared the rates of homicide and suicide in 17 countries and the relationship between personality differences and blood type in different countries [9] and found no significant association between blood type and introversion or extroversion, while Lester also noted that countries with high rates of anxiety and suicides also had a tendency to have low rates of type O and high rates of type AB. Since the 1980s and 1990s, studies on blood type and personality have more often used personality tests based on the five-factor model (Big Five, Big Five). Big Five [10] summarized the basic structure of previous personality tests as “Openness to experience”, “Conscientiousness”, and “Extraversion”. “Extraversion”, “Agreeableness”, and “Neuroticism ” five personality traits, which can cover basically all aspects of personality traits. Several studies based on the Big Five have shown [11,12] that blood type does not correlate with human personality. Mary Rogers et al. also tested the idea that Type O is more extroverted and optimistic, Type A is more agreeable, and Type AB is more self-aware by studying 180 pairs of men and women (12), and also specifically validated past studies based on the 16PF and EPQ that concluded that Type B is more emotional and emotionally unstable In particular, it was found that all of these views were untenable and that there were no significant differences in personality traits among blood types. These questionnaire-based personality studies all face similar problems. All personality questionnaires have been developed based on corresponding psychological theories. And over the last half century, psychological theories have evolved and changed, and even questionnaires such as the 16PF and EPQ, which have been in use for many years and are quite mature, are often subject to new theories and constantly face various challenges [2]. In addition, the accuracy of questionnaires is often influenced by subjects’ emotions, intelligence, alertness, or literacy, and the translation of the same questionnaire into different languages may cause biases in subjects’ understanding due to cultural differences. Despite the accuracy and reliability of questionnaires when studying personality, only a single questionnaire can still yield only more one-sided information [13]. This may also be the reason why these questionnaire-based studies of the relationship between blood type and personality often reach different conclusions. Another way of research is to infer the relationship between blood type and personality by analyzing the odds of developing psychiatric-psychological disorders in different blood types. Although certain personality traits [14] do have a close association with the development of some psychiatric disorders, the approach of inferring the relationship between personality and blood type by studying the relationship between psychiatric disorders and blood type is too indirect and seems to scratch the itch. The good thing is that the diagnostic criteria for psychiatric disorders are clearer, and the results of studies on different individuals are not always too different. In this regard, other less used blood groups are more likely to be associated with personality than ABO blood groups, and Elston et al. found that Rh and Gm blood groups may be associated with the onset of schizophrenia when they studied the incidence of schizophrenia in identical twins [15]. In contrast, a study of ABO blood groups [16] showed that type O was more likely to develop menopausal depression than other blood groups. Although these findings do not directly suggest a link between blood type and personality, they do suggest that blood type may have an impact on personality traits. Although scientists have different views on the relationship between blood type and personality, there is a consensus that personality is shaped by a combination of factors, including congenital factors, family upbringing, work and personal encounters. Even the Big Five [17] test results of genetically identical identical twins showed only about 50% similarity in five different personality traits. It is hypothesized that genetic factors have only about a 50% influence on personality, and the other half of the influence may depend on acquired factors. Genetic factors alone are very complex, and the blood type gene is only one of tens of thousands of genes in humans, so even if there is any correlation between blood type and personality, the degree of correlation is not more than 50% at most. Although it has been more than 110 years since the discovery of ABO blood type, blood type still remains a mystery to people. Scientists have demonstrated an association between ABO blood type and a variety of diseases [18], but the relationship between blood type and personality is still not well understood. Some studies have concluded that there is no relationship between the two, while others have suggested that blood type somehow influences personality and behavioral patterns. The conclusions of different researchers often contradict each other, but there is no evidence to support Takeji Furukawa’s claim that “the same blood type has a common temperament”. Therefore, it may be good to use blood type as a daily gossip, but it is not necessary to take it seriously. There are no two identical leaves in the world, and each person has a unique personality, so why do you have to apply it to a certain template?