Objective: To develop an assessment questionnaire for screen based behaviors among primary and secondary school students, so as to provide a basis for comprehensive assessment among the population. Methods: Nineteen experts were invited to take part in this study from August to September 2022. The initial framework and item pool of the assessment questionnaire were developed based on literature review and a series of guidelines and standards issued by the national education and health authorities, as well as relevant domestic and foreign guidelines, and were combined with existing assessment tools that were used to evaluate screen based behavior among these age groups. Experts in related fields were selected for two rounds of Delphi consultation to determine the dimensions, items and corresponding weights of the assessment questionnaire. Results: The response rates from two rounds of consultation were 95.0% and 100.0% respectively, the opinion submission rates were 89.5% and 63.2% respectively, and the authority coefficient ( Cr ) was 0.87. An assessment questionnaire was finally designed, consisting in 44 items and four dimensions, namely screen use type and time, screen use related health behaviors, safety and civilization in screen use, and reasonable arrangement of screen and non screen activities. The coefficient of variation( CV ) of each item ranged from 0.00 to 0.19, and the Kendall s W increased from 0.22 to 0.34( P <0.01). Expert opinions were in agreement and credible. Conclusion The designed assessment questionnaire can be used to comprehensively evaluate screen based behavior among primary and middle school students, and provides a basis for subsequent intervention measures to improve screen based behavior among this population.