Quantifying the dynamics of grasslands in Xinjiang's arid regions and their responses to key drivers is crucial for effective vegetation management in this ecologically fragile area. In the present study leaf area index (LAI) data collected during growing seasons from 2001 to 2020 were analyzed. Multiple analytical methods, including Sen's trend analysis, Mann-Kendall significance test, coefficient of variation, Hurst exponent, and structural equation modeling, were employed, to examine the spatiotemporal patterns of Xinjiang grasslands and their responses to topography, climate, and human activities. Spatial analysis revealed significant heterogeneity. The multi-year average LAI value from 2001 to 2020 was found to be 0.37 m⁻²·m⁻², characterized by higher values in the north and west, lower values in the south and east. LAI exhibited a fluctuating upward trend with an average annual growth rate of 0.004 a⁻¹. Trend analysis indicated that approximately 67.3% of the areas showed improvement, while 19.2% experienced degradation, with degraded areas primarily concentrated in the vicinity of the Ili River valley and Tacheng prefecture. Further, structural equation model revealed that topography, climate, and livestock factors impacted substantially spatial distribution of LAI in Xinjiang grasslands. Precipitation and wind speed were identified as dominant factors affecting LAI, with total path coefficients respectively of 0.34 and −0.32. Topography, through interactions with climate and livestock numbers, exerted a significantly positive impact on LAI. Overall, precipitation and altitude demonstrated positive influences, whereas wind speed, temperature, and solar radiation exhibited negative effects. Between 2001 and 2020, LAI of Xinjiang grasslands displayed marked fluctuations, primarily attributed to combined effects of natural environmental and human activity factors.