Objective To investigate the influence of coronavirus disease 2019(CoV-19)on children′s mental health,so as to provide basis for children′s psychological intervention under the emergency of major public health events. Methods A total of 20 579 children from 32 provinces and autonomous regions were randomly selected from February 12th to 20th,2020 via online questionnaire.Parents filled out self-made questionnaire on mental health status of children in the epidemic period of CoV-19.The general data were described and analyzed.Kruskal-Wallis H test,Spearman correlation analysis and multiple linear regression method were used to analyze the influencing factors of children′s mental health. Results 1)Among 20 579 children,73.70% had increasing parent-child interaction time,69.85% had increasing family density,63.63% used more electronic screens,37.39% had irregular work and rest,31.26% had excessive activities,and 20.37% had abnormal sleep.2) Significant difference on children′s behavior scale was found among children with different residential areas (H=80.891,P<0.001).3)There were statistically significant differences between parents of only children and non-only children in terms of emotion,family intimacy and epidemic pressure (H=14.824,10.914,18.254,P<0.01).Parents of children living in different places had significant differences on emotional,cognitive,family intimacy,epidemic pressure(H=68.398,50.240,56.027,54.250,P<0.001).4) Parents′ cognitive,emotion,epidemic pressure were negatively correlated with children′s behavior,family intimacy were positively related to children′s behavior (P<0.001),which all entered the regression equation (F=733.447,P<0.001,△R²=0.125) explaining 12.5% of the children′s behavior. Conclusions Children′s abnormal behavior during the epidemic of CoV-19 is mainly manifested in the prolonged electronic screen time,irregular work and rest,excessive activities and sleep problems.More attention should be given to preschool children in cities and towns during the epidemic period.Moreover,family environment is an important factor to maintain good psychological state of children during the epidemic.