Small testicular volume may be caused by congenital dysplasia, medications, varicocele and other reasons. 1. Testicular congenital dysplasia: the presence of chromosomal abnormalities, hypogonadotropic hypogonadism and other factors lead to testicular congenital dysplasia. 2. Drugs: radioactive substances, reproductive toxicity drugs will kill spermatogenic cells, resulting in apoptosis of spermatogenic cells, atrophy of spermatogenic tubules, reduction of tubular diameter, and reduction of testicular size. 3. Varicocele: Varicocele will affect the arterial blood supply and blood circulation of testis, resulting in testicular metabolic disorders, testicular atrophy and small size. In addition, small testicular volume can also be seen in other diseases, and it is recommended that patients go to the hospital in time to avoid delaying the condition.