Objective: To study the development of grip strength and its relationship with body weight, height and body composition in preschool children. Methods: Data was collected from 900 children aged 3-6 years in 4 preschools in Beijing during Sept. to Oct. of 2020. A questionnaire survey (birth weight, dietary and exercise), height, weight, bioelectrical impedance analysis of body composition and dominant hand grip strength tests were conducted. Partial correlational analysis, multivariate linear regression were used for association between grip strength and body composition. Results: The grip strength gradually increased with age, from (5.2±1.7) to (9.3±2.5)kg in boys ( F=57.93, P <0.01), and from (4.3±1.6) to (7.9±2.5)kg in girls ( F=48.77, P <0.01). Grip strength in boys were significant higher than that of girls ( t=6.42, P <0.01). The grip strength increased with weight status in boys ( F=5.35, P <0.01), with highest in obese group, followed by overweight and normal weight group. After adjusted for height, weight and birth weight, as well as maternal education, food consumption during the past week, grip strength in boys was positively correlated with fat free mass, upper limb muscle mass ( r=0.11, 0.09, P <0.05), and negatively correlated with body fat mass ( r=-0.18, P <0.05). Grip strength in girls was negatively correlated with body fat mass, and positively correlated with fat free mass ( r= -0.09, 0.09, P <0.05). Grip strength varied significantly by age, fat free mass and upper muscle mass in boys ( F=66.75, P < 0.01), and by age and fat free mass in girls ( F=150.81, P <0.01). Conclusion The grip strength can partially reflect changes in fat free mass for boys and girls, it also reflect changes in upper limb muscle mass for boys. Increases in fat free mass helps grip strength improvement.