Abstract: Objective: To establish methods to measure structured physical activity (SPA) and unstructured physical activity (USPA) based on video observation and acceleration sensors, and to explore the behavioral characteristics of SPA and USPA in young children. Methods: A total of 232 children aged 3-6 years from 9 kindergartners were recruited. According to the previous scales, expert interviews and Delphi method, the structured and unstructured physical activity assessment criteria for young children were formed. SPA and USPA measurement and evaluation methods were established by combining video observation and acceleration sensor ActiGraph GT3X-BT. Results: The structure-unstructured physical activity assessment criteria for young children included 2 type indicators, 3 regional indicators and 49 corresponding classification bases. The coordination coefficient (W) was 0.457 (P < 0.001), and the coefficient of variation (CV) was 0.00-0.24. The A priori consistency was 0.814. The effective rate of the measured samples was 91.8%. SPA accounted for 50.5% of total PA, and moderate-to-vigorous intensity physical activity in S and US each accounted for 18.1% of total PA. There were significant regional (urban and rural) and gender (male and female) differences. Conclusion: Structural-unstructured physical activity criteria for young children is an effective tool to assess the behavior characteristics of SPA and USPA in young children in China. Combined use of video observation and acceleration sensor technology can effectively establish SPA and USPA measurement methods in young children. The proportions of SPA and USPA in children are similar and affected by gender and region.