Objective To explore the relationship between social support and physical activity barriers in pregnant women with pre-pregnancy overweight or obesity, and analyze the multiple mediating effects of fear of falling and kinesiophobia on physical activity barriers, so as to provide evidence for developing interventions to reduce their physical activity barriers. Methods A total of 211 pregnant women with pre-pregnancy overweight or obesity were recruited by convenience sampling from August to December 2024. The general information questionnaire, the Social Support Scale for Pregnant Women′s Physical Activity, the Barriers to Pregnancy Physical Activity Scale, the International Falls Efficacy Scale and the Kinesiophobia Scale were used for this survey. A structural equation model was constructed to explore the causal pathways among social support, physical activity barriers, fear of falling and kinesiophobia, and identify the mediating paths of the variables. Results The scores of social support, fear of falling, kinesiophobia and physical activity barriers of participants were (82.07±10.43), (37.06±5.69), (41.09±4.74) and (91.84±16.45) respectively. Mediating effect analysis revealed that social support could directly predict physical activity barriers, with the direct effect accounting for 37.91% of the total effect. Fear of falling, kinesiophobia, and their chain mediating effect indirectly affected physical activity barriers, accounting for 25.39%, 22.44% and 14.26% of the total effect respectively. Conclusion Social support exerts a direct impact on physical activity barriers in pregnant women with pre-pregnancy overweight or obesity. Additionally, social support influences physical activity barriers through the chain-mediated effects of fear of falling and kinesiophobia. Early and precise assessment of social support, fear of falling, and kinesiophobia is essential.Individualized health education shall be carried out and social support shall be enhanced to guide pregnant women with pre-pregnancy overweight or obesity to self-regulate their fear of falling, relieve their kinesiophobia, and implement scientific and precise exercise management, so as to reduce their physical activity barriers.