The definition of small penis lacks a unified standard. The average length of the Chinese male penis is 8.08 cm, the circumference is 8.11 cm, and the average effective length is 12.4 cm. It is now generally accepted that the penis length of a mature newborn is no shorter than 1.9 cm; an adult penis length can be considered small if it is shorter than 4 cm when flaccid, 7 cm when elongated, and 9.5 cm when effectively erect. Micropenis is often due to low androgen levels caused by malfunction of the hypothalamic-pituitary-testicular axis or due to androgen receptor deficiency, and the cause needs to be sought for differential diagnosis. Experimental treatment can be done in early childhood with the application of androgenic preparations. If this is not effective, treatment decisions should be made only after the child has matured. Penis lengthening is indicated for patients with abnormally short penis caused by some disease that requires surgery. Penile lengthening should not be performed for cosmetic reasons in normal people with a short penis that does not affect urination or sexual intercourse. Penis lengthening is only an extension in appearance, the actual length does not change and only psychological satisfaction is achieved.