Abstract: Objective To investigate the physical fitness status and associated factors among 3 to 6 years old preschool children in Tongzhou District of Beijing City, and to provide evidence for promoting their physical development. Methods Based on the 2020 National Physical Fitness Surveillance data for Tongzhou District of Beijing City, a total of 416 children were included for standardized physical tests, including morphological, physiological, and fitness indicators, and questionnaire surveys. Independent sample t-tests and ANOVA were used to compare differences in physical indicators across groups, while multivariate linear regression models were applied to analyze influencing factors. Results The comprehensive rating score of children aged 3 to 6 years old in Tongzhou District of Bejing City was (79.98± 6.97) points, with a total physical fitness pass rate being 99.52%. The proportions of excellent, good, and pass grades were 37.50%, 39.90%, and 22.12%, respectively. The average heights for the 3 years old, 4 years old, 5 years old, and 6 years old groups in Tongzhou District were (102.13± 4.24) cm, (107.92± 4.66) cm, (115.43± 4.70) cm, and (119.16± 4.33) cm, respectively. The corresponding average weights were (16.63± 2.46) kg, (18.66± 2.54) kg, (21.60± 4.02) kg, and (23.46± 4.64) kg, respectively. Among children aged 3 to 6 years old, the average BMI was (15.95 ± 1.79) kg·m^-2, the body fat percentage was (21.92 ± 4.77)%, the average resting pulse rate was (95.24±9.7) beats per minute, The average grip strength was (5.74±2.07) kg, the average standing long jump distance was (78.12 ± 19.95) cm, the average sit-and-reach flexibility was (12.25 ± 4.65) cm, the average continuous two-foot jump time was (6.29 ± 2.55) seconds, the average 15-meter obstacle shuttle run time was (7.94 ± 1.30) seconds, and average balance beam walking time was (5.11 ± 2.25) seconds. The multiple linear regression analyses showed that higher composite fitness scores were significantly associated with female sex（b=1.72,95CI:0.42-3.01）, aged 4 years old and above（b=2.97,95CI:1.35-4.59）, mixed feeding（b=4.16,95CI:1.60-6.72） or breastfeeding （b=3.23,95CI:0.36-6.10） during infancy, taller paternal（b=0.16,95CI:0.02-0.30） and maternal （b=0.25,95CI:0.11-0.39） height, longer weekly moderate-to-vigorous physical activity duration（b=0.52,95CI:0.02-0.91）, and increased participation in sports interest classes（b=0.40,95CI:0.24-0.92） (all P<0.05). Conclusion The physical fitness of 3 to 6 years old in Tongzhou District of Beijing City is generally favorable, with sex, age, feeding patterns, genetic factors, and exercise interventions identified as key correlating factors. Comprehensive strategies are recommended to enhance early childhood physical health.