Abstract: The grassland ecosystem is one of the most important and widely distributed terrestrial ecosystems. Analyzing the grassland degradation and its influential factors holds great significance for guiding the conservation and sustainable use of grassland resources, as well as the restoration and reconstruction of degraded ecosystems. This study extracted information on the distribution of grassland in western Songnen Plain using an object-oriented classification method and a multi-layer decision tree while comprehensively considering the degradation of vegetation and soils. Using Landsat TM image data, this study constructed a comprehensive grassland degradation index (GDI) for 11 even years from 2000 to 2020, followed by the assessment of the spatiotemporal dynamics of grassland degradation. Using the standardized precipitation evapotranspiration index (SPEI) as an indicator of drought, this study analyzed the responses of grassland degradation to the spatiotemporal changes in climate-induced drought. The results indicate that from 2000 to 2020, grassland in the western Songnen Plain decreased to 1 024 700 hm² from 1 051 700 hm², with an annual decreasing rate of 0.1%. The grassland degradation showed a nonsignificant downward trend, with 81.7% of the grassland exhibiting a stable or downward degradation trend. The SPEI exhibited an increasing trend in both spring and summer, representing a downward drought trend with significant regional differences. Besides, there was a nonsignificant weak positive correlation between GDI and SPEI in both spring and summer. The results of this study will provide data support for the conservation and sustainable use of grasslands in the western Songnen Plain, while also holding active significance for managing and controlling the ecological and economic benefits of grasslands in this region.