We know that men ejaculate once in the past described a tablespoon, about 2-6 ml, if less than 2 ml is too little, more than 6 ml is too much, too much and too little may lead to fertility problems, here first said too little factors. 1, gonadal factors When the patient because of the body’s neuroendocrine axis, especially testicular dysfunction, causing androgen secretion is insufficient, so that the epididymis, seminal vesicles, prostate and other gonadal organs are stunted or secondary atrophy, can not normally secrete enough semen. When there is infection or other lesions in the accessory gland, especially the fluid secreted by the seminal vesicle gland and prostate gland can account for 95% of the semen volume, and once serious inflammation occurs, the semen volume will decrease. 2, ejaculatory duct obstruction The duct after the rendezvous of the vas deferens with the excretory duct of the seminal vesicle gland on the prostate gland is called the ejaculatory duct. The ejaculatory duct is about 1-2 cm long, completely embedded in the prostate gland, usually closed, and a strong rhythmic contraction occurs during orgasm, prompting the epididymal tail, the sperm of the vas deferens and the secretions of the seminal vesicle gland to be ejected in the posterior urethra. It can be caused by urethral stricture, urethral diverticulum, or it may be caused by infected edema. Treatment can eliminate the infection and, if necessary, surgical treatment to relieve the problem of obstructed sperm discharge. Other causes include tumors or cysts of the seminal vesicles, and surgical damage to the vas deferens. 2, retrograde ejaculation Bladder sphincter dysfunction, or local innervation disorder can occur partial retrograde ejaculation, retrograde ejaculation refers to when sexual intercourse reaches orgasm, although there is ejaculation action, but semen does not ejaculate forward from the urethra, but reverse backward into the bladder, because semen does not follow the normal path of external ejaculation and reverse into the bladder, resulting in a decrease in semen into the female body or completely absent, is one of the causes of male infertility. So when we learn that the patient just has a low semen volume, we have to look for the cause, which is usually ultrasound of the prostate and seminal vesicle glands, seminal plasma analysis, urinalysis (especially post-orgasmic urinalysis), sex hormone levels, and even nuclear imaging of the seminal vesicle glands, etc. Why does low semen volume cause male infertility? (1) Because semen is alkaline, if the amount of semen is too low, it can no longer adequately neutralize the acidic environment in the vagina, then the sperm will lose its vitality in this environment and cannot travel up to the fallopian tubes to unite with the egg, thus causing infertility. (2) Semen contains nutrients such as fructose, which provides energy for sperm activity. If the amount of semen is too low, then it will not be able to maintain sufficient nutrients for sperm activity and metabolism, making it impossible for sperm to travel upstream, resulting in infertility. (3) The amount of semen is too small to form a sufficient pool of semen in the posterior vaginal vault after sexual intercourse, making it difficult for sperm to enter the cervical canal, leading to infertility.