Objective: To investigate the effects of physical activity (PA) intensity and sedentary behavior (SB) on calcanues bone mineral density (BMD) in preschool children, so as to provide a basis for rationalizing the daily physical activity of preschool children to promote bone health. Methods: A total of 673 pre school children aged 3-6 years from nine kindergartens in Pingxiang City, Ganzhou City and Yingtan City of Jiangxi Province, were selected from September to December 2021 by using the whole stratified cluster random sampling method. The PA levels and SB were measured by using a three axis acceleration sensor, and left calcanues BMD was measured by an ultrasound bone densitometer. Multiple linear regression was used to explore the effects of changes in PA on calcanues BMD in pre school children of all ages. Results: Of the 673 preschoolers surveyed, 498 (74.0%) achieved an average of ≥60 min of moderate to vigorous physical activity (MVPA) per day, there were 265 boys (71.2%), and 233 girls ( 77.4 %). The difference between genders was not statistically significant ( χ 2=2.77, P >0.05). There was no statistically significant difference in the BMD test of the calcaneus bones of preschoolers by gender ( Z=0.42, P >0.05). The difference in BMD results of pre school children with 3, 4, 5 to 6 years was statistically significant ( H=2.65, P <0.05). Correlation analysis revealed a negative correlation between SB duration and calcaneus BMD ( r =-0.13), and a positive correlation between low intensity physical activity (LPA) duration, MVPA duration, and calcaneus BMD ( r =0.14, 0.25 ) ( P <0.05). Multivariate linear regression analysis showed that SB duration negatively correlated with calcaneus BMD, whereas LPA and MVPA duration positively correlated with calcaneus BMD ( P <0.05). Conclusions MVPA duration is positively correlated with the growth of BMD in the heel bone and negatively correlated with SB. The kindergartens can adjust their curricula according to the physical and mental developmental characteristics, gender and age differences of pre school children, increase the time of outdoor activities, and reduce the sedentary time to promote the bone health of young children.