Objective: To investigate the longitudinal association of plasma Irisin concentrations with changes in blood pressure (BP) levels among children,and to assess the moderating effect of physical activity (PA) or sedentary behavior (SB) on the relationship between Irisin levels and BP. Methods: Based on a cohort study, a cluster sampling method was used to select 3 651 school aged children from five schools in Guangzhou in 2017 at the baseline survey and follow up in 2019. Both at baseline and during follow up, PA and SB were assessed by validated questionnaires, and BP levels were measured by an electronic sphygmomanometer. A final sample of 521 children were enrolled based on the PA and SB at baseline. Plasma Irisin concentrations were measured by ELISA at baseline. Logistic regression analysis was recruited for exploring the associations of plasma Irisin concentrations with changes in BP. Moderating effects of PA and SB on the relationship between Irisin concentrations and BP were estimated using stratified analysis. Results: Logistic regression analysis indicated that there was no significant association between Irisin concentrations and changes in BP levels among children ( OR =0.98, P >0.05). After stratification for SB, Irisin levels in the low SB subgroup were inversely associated with changes in diastolic blood pressure ( OR=0.87, 95%CI=0.77-0.98, P =0.02). In addition, SB level had a moderating effect on the relationship between Irisin levels and the DBP changes ( P =0.01). Conclusion Increased Irisin concentration is associated with the decrease of DBP level among low SB children. Furthermore, SB level shows moderating role in the relationship between Irisin concentrations and changes in DBP levels.