In men, 90% of blood testosterone comes from the testes, and it reflects the function of the mesenchymal cells. Reduced blood testosterone is mostly seen in men with Turner syndrome, mesenchymal stromal cell hypoplasia, and undescended testis. Reasons for lowering blood testosterone 1, affecting embryonic development and promoting the growth and development of male sex organs. Testosterone can stimulate the growth and development of the prostate, penis, scrotum, urethral bulbous glands and other accessory sex organs; 2. Stimulate the growth of reproductive organs and the emergence of paraphysical signs. Testosterone can stimulate and maintain the male paraphilic sexual characteristics of medical`s education network collection, but also can produce and maintain a normal libido; 3, maintain spermatogenesis. After testosterone is secreted from interstitial cells, it can enter the seminiferous tubules through the basement membrane and bind with the corresponding receptors of spermatogenic cells to promote spermatogenesis; 4, affecting metabolism. Testosterone can promote protein synthesis, especially in muscle and bone; affect water and salt metabolism, favoring the retention of water and sodium in the body; increase calcium and phosphorus deposition in bone; 5, in addition, testosterone can stimulate the production of erythrocytes, so that the body of red blood cells increase. Abnormal physiological function in turn triggers abnormal blood testosterone concentration.