Whether it is an active test for preconception preparation or a passive test for fertility problems, a routine semen test is essential, as it is the most basic test to reflect male fertility, just like a routine blood test for your physical examination. Semen routine contains many parameters, including liquefaction time, PH value, sperm concentration, sperm vitality, sperm malformation rate and so on. Today, let’s get to know sperm density (concentration). Referred to as sperm concentration in the fifth edition of the WHO routine semen standards and sperm density in the fourth edition, both refer to the number of sperm per unit volume. Under normal circumstances this value is recorded in millions or even billions, which shows that the number of sperm is very large. What is the current normal standard for sperm density (concentration)? According to the 4th edition of the WHO semen quality standard, greater than 20*106/ml is considered normal; according to the 5th edition of the WHO standard, greater than 15*106/ml is considered normal. Firstly, the absolute value of the data must be obviously related to fertility; secondly, the semen volume needs to be considered, the product of semen volume and sperm density is the total number of sperm in one ejaculation; furthermore, it needs to be combined with sperm vitality, low sperm vitality, even if the sperm density is good, then there are still less sperm with good sperm vitality. In addition, it needs to be combined with a comprehensive evaluation of sperm malformation rate. Some semen samples with severe malformations have good sperm density, obviously, and this is where the problem needs to be focused first on the malformation rate, which is the same as the sperm viability reading. Also, is it true that more sperm density is better? It is not so. Too much sperm density is polyspermia, and collisions between sperm after activity can also diminish sperm motility. Finally, it should be reminded again that a routine semen examination cannot be based on a single examination, but requires repeated and comprehensive assessment. In severe cases of oligospermia, chromosomal and spermatogenic genes should be examined to rule out the possibility of hereditary diseases.