The penis used to be big and now it is shrinking may be due to physiological factors such as obesity, mental stress, or considered to be due to diseases such as erectile dysfunction. 1. Physiological factors: when the patient is excessively obese, the root of the penis will be buried in fat, and the penis appears to be smaller. Or nervousness and overwork may cause the penis to appear completely hard, manifesting as a previously large penis that is now shrinking. 2. Erectile dysfunction: The causes of erectile dysfunction are related to lack of sexual knowledge, bad sexual experience, trauma, Parkinson’s disease, high blood fat, penile sclerosis, long-term medication, high blood pressure and other factors. The patient will have an erection but the erection is not hard enough, which is manifested by a previously large and now shrunken penis. There are many reasons why the patient’s penis used to be big but now it is smaller, and it is recommended that the patient should consult the doctor in time so as to clarify the cause of the disease. Once the disease is diagnosed, the patient should actively cooperate with the doctor to take relevant treatment measures, so as not to delay the condition.