Abstract: Grassland phenology has a significant impact on the carbon balance of terrestrial ecosystems. However, the response of vegetation phenology to seasonal climate remains unclear. This study analyzes the response mechanisms of grassland phenology in China to seasonal climate, altitude, slope, and slope aspect from 2001 to 2019 using methods such as the Geodetector. The results are as follows: (1)The average start of season (SOS) was 172 days, showing an advancing trend at a rate of 0.2 days per year. The average end of season (EOS) was 258 days, showing a delaying trend at a rate of 0.35 days per year. (2)Temperature shows an accumulative effect on SOS, with an extended pre-season period expanding the region where temperature and SOS are negatively correlated. The influence of evapotranspiration and precipitation on SOS varies by season, with both factors generally showing a negative correlation with SOS. Seasonal temperature, precipitation, and evapotranspiration all positively correlate with EOS. (3)The response of SOS to altitude and slope shows a nonlinear trend. Below 4,000 meters, the delay rate of SOS is 1.85 days per kilometer; above 4,000 meters, the delay rate increases to 13.91 days per kilometer. When the slope is below 25°, SOS shows no significant change, but above 25°, SOS is significantly delayed. EOS advances with altitude at a rate of 0.1 days per kilometer. (4)The interaction between climate and terrain has a much lower impact on EOS than on SOS. Evapotranspiration-altitude interaction predominantly influences SOS, while precipitation-altitude interaction primarily drives EOS changes.This study provides a scientific basis for research on terrestrial ecosystem carbon cycling.