Background <p>Although handgrip strength (HS) is a useful indicator of various diseases, no study has yet investigated the effects of various influencing factors on HS over time. This study aims to analyze the spatiotemporal variation of relative HS, and its influencing factors, across diverse population groups in China.</p> Methods <p>Five national physical fitness surveys encompassing 831,878 adults aged 20–69 years were conducted in China from 2000 to 2020. Trained personnel recorded relative HS. A Bayesian spatiotemporal hierarchical model was employed to illustrate the spatiotemporal characteristics of HS, while a geodetector model assessed the impact and interaction of socioeconomic levels, living environments, and geographical factors on relative HS over time.</p> Results <p>From 2000 to 2020, the average relative HS in China declined, with a more pronounced decrease in men than women and among younger individuals relative to middle-aged and older counterparts. Spatial analysis revealed significant heterogeneity, with HS hot spots primarily in southern regions (excluding Tibet) and cold spots in the north. The 20-year decline in relative HS was primarily characterized by a more substantial decrease in individuals with initially higher HS. Before 2010, HS differences were primarily attributed to geographic factors, whereas post-2010, the influence of socioeconomic factors increased.</p> Conclusions <p>There is a need to address the greater decline of HS in men and especially in young individuals. China should implement targeted interventions in specific regions to mitigate the rapid decline in HS, taking into consideration diverse regional socioeconomic factors.</p>