A man’s lack of semen may be caused by physiological reasons, or it may be caused by pathological factors, such as retrograde ejaculation, erectile dysfunction and other reasons. 1. Physiological factors: the lack of semen may be caused by men who are too nervous or who have recently been overworked, which can usually be relieved after getting enough rest. It is also possible that the man has not yet reached orgasm, so naturally there is no semen production. 2. Pathological factors: (1) Retrograde ejaculation: Retrograde ejaculation refers to the situation where semen is not discharged from the urethra after reaching orgasm, but is discharged into the bladder retrograde. It may be related to a variety of factors such as congenital developmental abnormalities, surgery, injury, medication or disease. (2) Erectile dysfunction: when patients have erectile dysfunction, it will be manifested as not being able to have a normal erection during sexual intercourse or the degree of erection is insufficient, etc. Patients are usually accompanied by symptoms such as decreased libido, abnormal ejaculation, and lack of orgasm. When men do not have semen, they should seek early medical examination so as not to affect the male reproductive function.