Objective To analyze the effects of air pollutants on male semen quality and different stages of sperm development in Taiyuan. Methods Totally 7 614 men who were admitted to the Reproductive Department of the First Hospital of Shanxi Medical University from January 1 to December 31, 2019 were enrolled. Their age, semen collection season, and semen parameters were recorded. At the same time, the monitoring data of six air pollutants (SO2, N02 CO, 03, PM25, and PML0) were collected, and the exposure of air pollutants in the whole developmental period (0 to 90 days before semen collection) and three critical developmental periods (0-9 days, 10-14 days, and 70-90 days) were calculated. Nonparametric Mann-Whitney U test was used to compare the data difference between qualified and unqualified semen parameters. The generalized estimation equation was used to explore the effects of six kinds of air pollutants on the quality parameters of each sperm at different stages of sperm development. Results During the whole period of sperm development, the exposure concentrations of S02!1 NO2, O3, and PM25 were different between the qualified and unqualified groups of normal sperm morphology. The exposure to PMl()at 10 and 14 days before semen collection was positively correlated with semen volume (07=1.245, 95%CZ: 1.057-1.467), sperm concentration (Oi=1.247, 95%CI: 1,027-1.514), total sperm count (OR=1.385, 95%CI: 1.167-1.643), total motility (Oi=L236, 95%CZ: 1.085-1.409), and forward movement (Oi=L207, 95%CZ: 1.059-1.376). The O3 exposure was positively correlated with sperm concentration (02 = 1.250, 95%CI: 1.002-1.55& OR = 1.173, 95% CI: 1.025 -1343), total sperm count (Oi=1.255!) 95%CI: 1.026-1.537; OR二 121 & 95%CI: 1.074-1380), and normal sperm morphology (O/=1.295, 95%CIi 1.047-1.602; OR二1229, 95%CI: 1.076-1.404). Conclusion Exposure to air pollutants increases the risk of unqualified semen parameters at all stages of sperm development, and the critical window period focuses on 10-14 days before semen collection, which is the developmental stage of sperm motility. PMLo and O3 are the main reproductive toxins affecting the decline of male sperm quality in Taiyuan, which need to be paid attention to. [ABSTRACT FROM AUTHOR]