Objective To analyze the causes of changes in the prevalence of respiratory diseases and the reason for changes in medical visit behavior of children in Zhejiang Province during the winter and spring seasons of 2019-2021, and to provide important reference for the allocation of hospital resources, implementation of hierarchical diagnosis and treatment, and epidemic prevention and control. Methods A retrospective study was conducted on 256 937 outpatient medical records from January 23rd to April 23rd of each year from 2019 to 2021 at the Children's Hospital Affiliated to Zhejiang University School of Medicine. Statistical methods were used for data analysis. Results A total of 256 937 cases were selected in the present study, including 157 000 cases in 2019, 22 192 cases in 2020, and 77 745 cases in 2021. The number of patients to the Children's Hospital of Zhejiang University School of Medicine from outside Hangzhou accounted for 41.74%, 14.36% , and 18.53% in 2019-2021, respectively. For 0~2 years old , 3~6 years old , and 7~14 years old groups , the percentages of patients with upper respiratory tract infections were 49.54%, 45.95%, and 46.74%, respectively ; with lower respiratory tract infections were 42.90% , 31.76% , and 22.95% ; with influenza were 2.23% , 3.15% and 4.09%; and with asthma were 1.37%, 5.08%, and 8.15%, respectively. Conclusion From 2019 to 2021, there have been significant changes in the total number of respiratory diseases in children, the proportion of disease types, and the proportion of children's geographical composition. It is necessary to continue to monitor children's respiratory diseases, grasp the dynamic changes in their medical visits in real time, adjust the hospital admission model , implement the graded treatment policy, and promote the prevention and control of respiratory diseases in children.