Understanding the impact of climate change and human activities on vegetation is of great significance to the sustainable development of terrestrial ecosystems. Based on monthly MODIS leaf area index and meteorological data, the trend and partial correlation analysis, time-lag and cumulative effects analysis, and the improved residual analysis were used to evaluate the LAI dynamics of vegetation in the growing season of Songliao River Basin from 2001 to 2021, explore the impact of climate and human drivers on vegetation under the premise of taking time-lag and cumulative effects into account. The results showed that: (1) the overall distribution pattern of LAI in Songliao River Basin was low in plain and high in mountain area. In the past 21 years, the vegetation LAI showed an upward trend in fluctuations, and the future vegetation change trend will be mainly continuous improvement, but there is still a risk of degradation in the grasslands of western Inner Mongolia and some areas of Daxing'an Mountains and Xiaoxing'an Mountains. (2) Vegetation LAI was positively correlated with precipitation, and vegetation growth was more sensitive to precipitation than air temperature. The time effects of the LAI change varied with climate factors, land cover types and vegetation zoning. The main time effects of LAI on air temperature were 2 month lag and 0-1 month accumulation, while for precipitation, there was no significant lag and 1 month accumulation. (3) The combined effects of climate change and human activities were the main reasons that affected the dynamics of vegetation LAI in Songliao River Basin, and their contributions to vegetation change accounted for 41.7% and 58.3%, respectively. When considering time-lag and cumulative effects at the same time, the explanation degree of climate factor to vegetation growth was improved.