A man's penis is different from his height, fat and thin, and his facial features are different, with different lengths and uneven thickness. Shi has measured the penis size of China 14 12 healthy young men and the penis erection length of 126 healthy men. The results show that the longest is 19.5 cm, the shortest is 3 cm, and the average is 8.375 cm. Maximum circumference 14 cm, minimum 2.5 cm and average 7.3cm.. The longest is 23 cm, the shortest is 8 cm, and the average is 12 cm. Maximum circumference during erection 14 cm, minimum 8 cm, average10.75cm.. The penis length of 1000 normal adult males investigated by Liu Guozhen et al. is: the normal length is 4.9 ~ 8.6 cm, with an average of 6.55 cm, the longest is 1.6 cm, and the shortest is 3.7 cm. Wu Weicheng et al. measured the penises of 2547 male college students 16-25 years old, with an average length of 7.43 cm and an average circumference of 8. 17 cm. The average penis elongation is 13.34 cm, which is close to the calculated erection length 13.08 cm, so the elongation can represent the length after erection. It can be seen that there are some differences in the measurement results of different authors, and the results are also influenced by regions and nationalities. In addition, the penis length of the same person is not constant under normal circumstances, such as tension, cold or severe fatigue, which will shorten the penis.