Some men simply rely on visual inspection to determine their penis is shorter than others, for which they feel inferior, and worry about whether they can have a normal sex life after marriage and whether they can have children. These are unnecessary worries. Because, the real standard should be to evaluate the functional size of the penis by the efficiency of erection, and the expansion factor of the penis after erection is usually 100%-150%. The penis varies widely in length under normal conditions, while the difference in length during erection is small and generally achieves the size needed for normal sexual function. There are racial differences and individual differences in the size and length of the penis, and each person enters puberty at a different age, and there are differences in development, so the length and thickness of the penis of young men of the same age will be somewhat different even after full development and maturity, which is normal. The penis is too short that is really small penis is rare. Domestic Shi Chengli has measured the penis size of 1412 cases of healthy young men in China and the erect length of 26 cases of healthy men. The results showed that the longest length at normality was 14.5 cm. The shortest was 4 cm, with an average of 8.375 cm, and the circumference was a maximum of 12 cm, a minimum of 4.5 cm, and an average of 8.3 cm. The longest length is 16 cm when erect, the shortest is 9 cm, and the average is 12 cm. It is normal for an adult man’s penis to be 4 cm and 14 cm long in the non-erect state. Both 9 cm and 16 cm are normal when erect. From the point of view of sexual function, the length and thickness of the penis have a relationship with the quality of sexual life. However, it does not play a decisive role. The key to sexual satisfaction is not the size and length of the penis, but mainly depends on the psychological state of the two parties involved in sexual intercourse, their emotional communication and physical and mental state.