Semen consists of spermatozoa and seminal plasma. Seminal plasma is not a single source, but a mixture of the respective secretions of the prostate gland, seminal vesicle gland, urethral gland and epididymis. These secretions have different acidity and alkalinity, and when mixed, they form the acidity and alkalinity of semen, which is the pH of semen, indicating the acid-base state of semen and also reflecting the secretion function of different accessory sex glands, mainly the secretion function state of prostatic fluid and seminal vesicle glands. Prostate fluid is milky white, pH 6.5, small amount, generally 0.5~1ml, constituting about 1/3 of the volume of semen, the first part of the ejaculated semen, and does not coagulate. The components of prostatic fluid can stimulate sperm vitality and have antibacterial and immunosuppressive effects. The seminal vesicle gland fluid is milky yellow, pH 7.2~8.0, with a large amount, usually more than 2ml, constituting about 2/3 of the volume of semen, which is the last part of the ejaculated semen, and generally this part of the fluid forms clots quickly. Sperm vesicle gland fluid has prostaglandins in its composition, which can promote the contraction of the smooth muscle of the urethra in men to facilitate ejaculation, and can cause the vagina of the woman to contract after sexual intercourse to promote sperm movement. The seminal vesicle gland fluid also contains energy-supplying substances for sperm. Urethral glandular fluid is clear and resembles dilute egg white, and the amount is very small. It is secreted during sexual arousal and is the initial part of semen, lubricating the urethra to facilitate the passage of subsequent fluids. Epididymal fluid is yellow, viscous and very small in volume. It constitutes the extracorporeal environment for sperm in the epididymis and participates in sperm maturation. A very small amount of urine is sometimes left in the penis and is also mixed into the semen during ejaculation. When urine briefly touches the sperm, it can cause a hypotonic swelling effect on the sperm tail, resulting in a slight coiling of the tail. The above fluids are mixed together during ejaculation and determine the pH of semen. normal semen pH is 7.2 to 8.0. if the pH is less than 7.0 or greater than 8.0, it is abnormal. If the pH of semen is less than 7.0, most of the seminal glands do not secrete enough fluid or there is no fluid at all. The reason for this is due to underdevelopment or absence of sperm, and if there are sperm in the semen, they will die quickly. If the pH of semen is greater than 8.0, it is mostly related to prostatitis, and the spermatozoa will have abnormal movement status and shortened survival time. Some men may have varying degrees of calcification of the prostate gland or calcification of the seminal vesicle gland, which can reduce the amount of fluid produced by the gland and can affect semen pH, and should be noted when performing semen examinations.