Objective To analyze the changes of disease spectrum in pediatric inpatients before and after the outbreak of coronavirus disease 2019 (COVID-19). Methods The data of gender, age, habitual residence, diagnosis and other relevant information of 1 931 hospitalized children in Department of Pediatrics, The First Affiliated Hospital of Naval Medical University (Second Military Medical University) from Feb. 2019 to Jan. 2020 (1 year before the COVID-19 epidemic) and 618 hospitalized children from Feb. 2020 to Jan. 2021 (1 year after the COVID-19 epidemic) were collected. The total number, habitual residence, gender and disease spectrum of hospitalized children 1 year before and 1 year after the COVID-19 epidemic were statistically analyzed. Results The number of hospitalized children decreased by 68.00% (1 313/1 931) 1 year after the COVID-19 epidemic. The number of hospitalized children from other provinces and cities was decreased (17.80%[110/618] vs 29.00%[560/1 931]) and there was significantly difference in the distribution of habitual residence of hospitalized children between 1 year before and 1 year after the COVID-19 epidemic (P<0.01). One year after the COVID-19 epidemic, the number of children with respiratory diseases decreased by 92.04% (971/1 055), and the proportion was also decreased (13.59%[84/618] vs 54.63%[1 055/1 931]); the number of children with endocrine system diseases increased by 20.71% (29/140), and the proportion was increased (27.35%[169/618] vs 7.25%[140/1 931]); the number of children with neonatal diseases decreased by 43.01% (166/386), but the proportion was increased (35.60%[220/618] vs 19.99%[386/1 931]). Compared with 1 year before the COVID-19 epidemic, there were significant differences in the proportions of respiratory diseases, endocrine system diseases and neonatal diseases in hospitalized children 1 year after the COVID-19 epidemic (all P<0.01). The age distribution of hospitalized children 1 year before and 1 year after the epidemic of COVID-19 was different (P<0.01), and the number of hospitalized children was also different in different seasons (P<0.05). One year after the epidemic of COVID-19, the number of hospitalized children with respiratory diseases was decreased most significantly, and the number of children with pneumonia decreased by 93.71% (655/699), with a significant difference found in the proportions of pneumonia between 1 year before and 1 year after the COVID-19 epidemic (52.38%[44/84] vs 66.26%[699/1 055], P<0.05). Compared with 1 year before the COVID-19 epidemic, the proportion of endocrine system diseases such as short stature/growth retardation was decreased and the proportion of precocious puberty/early puberty development was increased 1 year after the COVID-19 epidemic (P<0.05). Conclusion The COVID-19 epidemic has led to a significant decrease in hospitalized children in department of pediatric, especially in the proportion of respiratory diseases, but it has led to an increase in hospitalized children with endocrine system diseases, suggesting that epidemic prevention and control measures can effectively reduce respiratory diseases requiring hospitalization, but may increase precocious puberty and early puberty development. These changes should be considered by department of pediatrics in general hospitals.