Objective: To explore the relationship between ambient PM 2.5 level and outpatient visits of children with respiratory diseases in a megacity, Zhengzhou, in central China., Methods: We collected daily outpatient visit data, air pollutant data, and meteorological data at the monitoring points of Zhengzhou from the time period 2018 to 2020 and used Spearman's rank correlation to analyze the correlation between children's respiratory outpatient visits and air pollutants and meteorological factors. Generalized additive models were used to analyze the association between PM 2.5 exposures and children's respiratory outpatient visits. A stratified analysis was further carried out for the seasons., Results: From 2018 to 2020, the total number of outpatients with children's respiratory diseases was 79,1107, and the annual average concentrations of PM 2.5 , PM 10 , SO 2 , NO 2 , CO, and O 3 -8h in Zhengzhou were respectively 59.48 μg/m 3 , 111.12 μg/m 3 , 11.10 μg/m 3 , 47.77 μg/m 3 , 0.90 mg/m 3 and 108.81 μg/m 3 . The single-pollutant model showed that the risk of outpatient visits for children with respiratory disease increased by 0.341% (95% CI : 0.274-0.407%), 0.532% (95% CI : 0.455-0.609%) and 0.233% (95% CI : 0.177-0.289%) for every 10 μg/m 3 increase in PM 2.5 with a 3-day lag, 1-day lag, and 1-day lag respectively for the whole year, heating period, and non-heating period. The multi-pollutant model showed that the risk of PM 2.5 on children's respiratory disease visits was robust. The excess risk of PM 2.5 on children's respiratory disease visits increased by 0.220% (95% CI : 0.147-0.294%) when SO 2 was adjusted. However, the PM 2.5 effects were stronger during the heating period than during the non-heating period., Conclusion: The short-term exposure to PM 2.5 was significantly associated with outpatient visits for children's respiratory diseases. It is therefore necessary to strengthen the control of air pollution so as to protect children's health., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Liu, Wang, Qian, Wei, Yang, Wan and He.)