Objective: To evaluate the status of dietary diversity and determinants among school age left behind children. Methods: A total of 501 children aged 9-10 years in Sheyang Mini Cohort Study were enrolled from Sheyang City in Jiangsu Province during 2019. A questionnaires survey was administrated to collect left behind and socioeconomic information. Twenty four hour dietary recall survey was conducted, dietary diversity score (DDS 10 and DDS) and food variety score (FVS) were computed according to Food and Agriculture Organization (FAO). Weight and height of children were measured and sex and age standardized body mass index was used to define obesity. Multivariable regression models were preformed to explore the determinants of dietary diversity in school age left behind children. Results: The proportion of left behind children was 40.9%. The mean value and standard deviation of three kinds of dietary diversity score (DDS 10 , DDS, FVS) in left behind children were (5.69±1.31)(6.55±1.44) and (13.48± 4.23 ), respectively. All of these were lower than that in non left behind children (DDS 10 :5.99±1.29; DDS:6.79±1.40; FVS:14.15±4.22). Significant difference in DDS 10 between left behind and non left behind children was observed ( P =0.01). The results of multivariable regression demonstrated that gender, passive smoking, family education level and family economic status were related to dietary diversity scores ( P <0.05). Conclusion Dietary diversity in school age left behind children was not optimistic and gender, passive smoking, parental education level, family economic status and left behind situation play a critical role in dietary diversity among these children.