Objective: To understand sleep behavior among primary and middle school students and its impact on overweight and obesity changes, to provide evidence for developing obesity prevention and controlling strategies in children and adolescents. Methods: Primary and middle school students from three cities in Zhejiang Province who participated in questionnaire surveys and physical measurements in both 2017 and 2019 were selected. A follow up dataset of 605 students was developed and the relationship between sleep duration and body mass index was analyzed. Results: From 2017 to 2019, BMI Z scores for male and female participants increased by 0.24 and 0.13, respectively. BMI Z scores increased by 0.29 in students of 9-12 years old and increased by 0.11 and 0.25 in urban and rural students, respectively ( P <0.05). The prevalence of insufficient sleep duration increased from 37.0 % to 41.8% simultaneously ( χ 2=3.68, P =0.06). After adjusting for confounding factors, the BMI Z score of students with insufficient sleep was 0.20 higher than those with sufficient sleep duration ( P <0.01). Compared with participants who had sufficient sleep duration from 2017 to 2019, participants whose sleep duration changed from sufficient to insufficient, and those who always had insufficient sleep duration increased by 0.23, respectively ( P <0.05). Conclusion Insufficient sleep duration is a risk factor for obesity. Shortened sleep duration is related to weight gain, and maintaining sufficient sleep duration may reduce the risk of obesity in children and adolescents.