1. Morphological development of sexual organs: Male genital organs are divided into two parts: internal and external. The internal genitalia include testes, vas deferens and accessory glands, while the external genitalia include scrotum and penis. There are great individual differences in the sexual development of boys during puberty, but the order of appearance of the signs is roughly similar: the testes are the first to develop, and the penis begins to develop one year later, along with the sudden increase in height. The average age of testicular enlargement is 11.5 years old (between 9.5 and 13.5 years old), which is actually only 6 months to 1 year later than the age of female breast development, and can reach 15 to 25 ml at the age of 18 to 20. On average, the growth spurt begins at about 12.5 years of age and increases from less than 5 cm before puberty to about 12-13 cm at the end of puberty within 2 to 3 years. The development of male external genitalia (testes, scrotum and penis) can be evaluated comprehensively according to Tanner’s five-stage staging criteria. Stage I (infantile): from birth to the beginning of puberty, the size of the genitalia increases slightly, but there is little change in appearance; Stage II: the scrotum begins to increase in size, the skin becomes slightly red, and the texture changes slightly; Stage III: the length of the penis increases, the diameter increases, and the scrotum further increases in size; Stage IV: both the length and diameter of the penis increase more significantly, the head of the penis forms, the scrotum continues to increase in size, and the skin color Stage V (adult type): the shape of the genitalia becomes adult type. 2. Development of sexual function: As the testicles grow, the reproductive function of puberty also begins to develop. Seminal emission is one of the important signs that male reproductive functions begin to develop and mature during puberty, and is also a normal physiological phenomenon that occurs in healthy males in mid- and late-adolescence. The first seminal emission usually occurs between the ages of 12 and 18, about two years after the age of female menarche. Most of the first seminal emission occurs in summer, and the initial semen is mainly prostatic fluid, with few viable mature sperm; at the age of about 18, along with the further development of testicles and epididymis, the semen composition gradually approaches that of adults. After the first ejaculation occurs, the growth rate of height gradually slows down, while the testes, epididymis and penis develop rapidly and approach the adult level. 3. Development of secondary sexual characteristics: In addition to pubic hair, axillary hair, beard and hair changes, there are also voice changes and the appearance of laryngeal nodes. Pubic hair usually appears around 11 to 12 years old, axillary hair appears 1 to 2 years later, beard starts to emerge in another year or so, the frontal hairline moves back, and the facial profile evolves from childhood to adulthood. As androgen levels rise, the laryngeal nodes increase in size, the vocal cords become thicker and longer, and vocal changes generally occur after the age of 13. The vast majority of boys complete the development of all secondary sexual characteristics by the age of 18. It should be noted that more than half of boys will have “transient” breast development, which usually begins on one side with a small hard lump under the areola that is mildly elevated and painful to the touch, and usually subsides in about six months. If it does not subside, further examination should be done.