Approximately 10% of China’s grasslands are severely degraded and 90% of them are overgrazed. To protect ecosystems and boost human well-being, payments for ecosystem services programs have been implemented to generate win-win outcomes for both pastoralists and the grasslands. Taking a payment for ecosystem services program in Damao County, Inner Mongolia as an example, our study evaluated the ecological effects of the Grassland Ecological Compensation Policy (GECP) based on historical trend at the pixel, parcel, and county levels. We also evaluated the socioeconomic effects of GECP using both objective and subjective well-being at the household level. Our results show that: (1) at the pixel level, the percentages of additionally increased Normalized Difference Vegetation Index (NDVI) and Net Primary Production (NPP) were 93.4% and 93.3% after GECP implementation, corresponding to the average additional effects of 0.08 and 58.99 g C/m2, respectively. At the parcel level, the GECP additionally increased NDVI between 0.02-0.17 (average of 0.08) and increased NPP between 28.36-115.15 (average of 60.30) g C/m2, respectively. At the county level, the GECP additionally increased grassland NDVI and NPP by 0.07 (~3.4% annually) and 53.63 g C/m2 (~4.5% annually) from 2008 to 2020, respectively; and (2) the GECP implementation significantly improved pastoralists’ objective well-being (P < 0.01) while the effects on subjective well-being indices were mixed. Our results also show that GECP effects on objective and subjective well-being significantly differ from households with large rangeland to those with small rangeland. We further discussed the experience, challenges, and opportunities of GECP. The long-term sustainability of GECP, particularly socioeconomic sustainability, still remains challenging and relies on guiding pastoralists to find alternative livelihoods. For future research and policy improvement, we call for the establishment of a better policy compensation mechanism that jointly considers the ecological effectiveness, economic efficiency, and social equity.