Common causes of dilute semen include frequent sexual intercourse, high scrotal temperature, prostatitis, seminal vesiculitis, vitamin E and other trace element deficiency, heavy alcohol consumption, smoking, and long-term application of androgens. Semen is composed of seminal plasma and spermatozoa, with seminal plasma accounting for more than 90% of the volume of semen. Spermatozoa are produced by the testes, mature in the epididymis and are discharged through the vas deferens. Seminal plasma is mainly a mixture of fluids secreted by accessory glands such as the prostate, seminal vesicle and urethral bulb glands, and also includes a small amount of testicular fluid and epididymal fluid. Dilute semen refers to thin semen like watery body fluid, but it does not necessarily mean that the sperm count is declining, and routine semen examination is required. Except for frequent sexual intercourse with multiple ejaculations, which leads to insufficient seminal plasma secretion, resulting in thin semen. The presence of thin semen in the natural state should still be taken seriously to clarify whether there is a primary disease. It is recommended to perform routine semen examination to exclude thin semen caused by infection factors and to clarify whether there is a decrease in sperm quality in time for symptomatic treatment. In summary, the reason for semen thinning out of frequent sex and other physiological reasons, often appearing semen thinning should cause attention, clear cause semen thinning primary disease, timely symptomatic treatment.