In this study, we assessed the effect of seasonal variation on the semen quality in Chinese by using the average highest temperature (AHT) of the ejaculation day for partitioning season periods. A total of 13 635 semen samples were collected and analysed according to the AHT of the ejaculation day. Semen volume, sperm concentration and the percentage of spermatozoa with normal morphology in midsummer (AHT > 30 °C) were significantly lower than those in other periods of the year. Sperm motility with AHT 10–20 °C in winter and spring was significantly higher than that in other seasons. The percentage of head defects spermatozoa with AHT < 10 °C in winter was significantly lower than that in other periods. We observed that there was a significant effect of season on the semen parameters. Highest environment temperature of the day may be a determining factor for the seasonal variations in semen quality.