Objective: To determine the influencing factors of electronic screen time of urban preschoolers before and after the COVID-19 outbreak, so as to provide a scientific basis for the control of digital screen use and early prevention of myopia among preschoolers. Methods: Using multi stage cluster random sampling method, a cross sectional survey of 8 244 kindergarten students in a district of Shanghai was implemented, through parent questionnaire collecting the time child spent on various electronic screens before and after the COVID-19 outbreak, estimated the weighting screen time, and emphatically analyzed the relationship between family electronic screen supervision behavior and preschoolers weighting screen time. Results: The proportion of daily over use time on average of mobile phones, computers and TV/projection screens among the surveyed preschool children during COVID-19 was 30.52%, 51.40% and 56.82%, respectively. On school days before the epidemic, the proportion was 21.94%, 41.80% and 47.51% respectively. After controlling for primary covariates, parents frequent control of children s electronic screen use, parents guidance for electronic screen use were significantly associated with lower weighted screen refractive time ( OR =0.60-0.77, P < 0.05 ). The use of electronic screen when parents accompanied their children, the use of electronic screen time by parents but not strictly implemented were significantly associated with higher weighted screen refractive time and increased screen refractive time ( OR =1.18-1.80, P <0.05). Conclusion Urban preschoolers electronic screen time was high during and before COVID-19. In the control measures of preschool children s electronic screen time, attention should be paid to the management of electronic screen use within the family and parents role model.