<p>Forest soils hold the largest carbon on land and play a key role in global carbon balance, climate change, and the stability of terrestrial ecosystems. Consequently, fluctuations in soil organic carbon (SOC) significantly influence atmospheric CO₂ concentrations. Although carbon emissions induced by land-use change (LUC) have been extensively studied and many reports indicate SOC declines following deforestation, our analysis reveals more complex patterns. We conducted a meta-analysis of 548 observational datasets from 46 peer-reviewed studies spanning climatic gradients (semi-arid to humid, tropical to temperate) to identify global patterns and drivers of SOC changes induced by primary forest LUC to grassland. Land-use conversion increased mean SOC stocks by 3.35&#xa0;Mg·ha⁻¹ (13.30%), with significant regional variation: tropical systems exhibited moderate gains (2.05&#xa0;Mg·ha⁻¹, 7.70%), while temperate regions showed substantial increases (5.19&#xa0;Mg·ha⁻¹, 24.70%). Depth-specific analysis revealed differential accumulation across soil layers: 0–20&#xa0;cm (+ 3.02&#xa0;Mg·ha⁻¹), 0–30&#xa0;cm (+ 3.05&#xa0;Mg·ha⁻¹), and &gt; 30&#xa0;cm (+ 5.18&#xa0;Mg·ha⁻¹). Increases in deeper layers may reflect root allocation patterns and texture-dependent stabilization mechanisms. Both mean annual temperature (MAT) and mean annual precipitation (MAP) were significantly correlated with SOC changes (<i>P</i> &lt; 0.05), with negative associations observed between these climatic variables and changes in carbon stocks. These findings are consistent with previous studies indicating that MAT and MAP critically influence ecosystem carbon dynamics. A significant interaction effect between MAT and MAP on SOC stock changes was also identified (<i>P</i> &lt; 0.05). Our results enhance understanding of carbon balance dynamics following LUC in primary forests and provide a scientific foundation for soil carbon management strategies under global change scenarios.</p>