Ground-source heat pumps (GSHPs), as a renewable energy technology capable of replacing traditional heating and cooling systems while reducing CO₂ emissions, have attracted significant attention from researchers in China. The coefficient of performance (COP), a key metric for evaluating the efficiency of GSHP systems, is heavily influenced by environmental factors, particularly groundwater temperature. This study conducts a comprehensive assessment of GSHP performance across all provincial capital cities and municipalities in China. Simulation results for COP across five climate zones indicate that the heating COP typically ranges between 5 in the sever cold zone and 6 in the hot-summer and warm-winter zone. The systems demonstrate significant potential for CO₂ emission reductions in heating applications, achieving average annual savings of 74.01 tons compared to coal-based heating and 32.79 tons compared to natural gas-based heating. The findings highlight pronounced regional disparities in GSHP performance across China’s diverse climate zones. Notably, the cold zone exhibits the highest potential for CO₂ emission reductions. However, considerable variations in system performance are observed among cities within the same climate zone, particularly in the severe cold zone, where CO2 emission reductions span a range from 33 to 233. But the proportion of CO₂ emission reductions attributed to fuel-based heating is consistently stable at 25% nationwide, no matter what thermal demand and climate zones.