As babies grow up, liquid food gradually fails to meet the nutritional needs of the organism, and the challenge that guardians must face is to complete the transition from liquid to solid food within one year of age. Whether milk or breast milk for infants after 6 months of age, its energy density is too low, single nutrition, and can no longer independently play the role of nutritional guardian. Moreover, eating liquids without chewing and with little oral movement is not conducive to speech development. However, highly evolved human beings are not able to adapt to the direct conversion from liquid to solid, and need to transition through paste-like food, that is: liquid – paste – solid “three-stage rocket theory”. Strictly speaking, the term is not “complementary foods”, but “the introduction of transitional foods”. “Supplementary food” is easily misunderstood as “supplementary, secondary, optional” food. Purpose: 1. To supplement nutrition; 2. To prepare for weaning; 3. To develop good eating habits. Principles: 1. from less to more; 2. from fine to coarse; 3. from thin to thick; 4. from one to many; add gradually under the condition that the infant is healthy and has normal digestive function. Note: 1. Don’t ignore the “eating skills” column in the table, people and animals are born sucking on nipples and pacifiers. A link. 2, the start of prematurity, generally no earlier than the correction of the age of months (calculated from the beginning of the expected date of birth) 4 months, no later than 6 months.