With the global climate change in recent decades, the Qinghai-Tibet Plateau is in the process of warming and wetting, and the vegetation on the Qinghai-Tibet Plateau has undergone significant changes. Based on the normalized vegetation index (NDVI) from satellite remote sensing observations, we used the boosted regression tree approach (i.e., a machine learning algorithm) to quantitatively examine the relative importance of the environmental factors including temperature, precipitation, soil moisture, and solar downward shortwave radiation on influencing the vegetation dynamics in the growing seasons on the Qinghai-Tibet Plateau from 1982 to 2015. The results showed that:(1) the spatially averaged NDVI and precipitation on the Qinghai-Tibet Plateau in the growing seasons (from June to September) increased during 1982-2015, with the trend values of 1.265×10^-4 a^-1 and 0.746 mm/a, respectively, but the trends were not significant (P>0.05); both the spatially averaged temperature and the spatially averaged soil moisture in the growing seasons significantly increased during 1982-2015 (P<0.01), with the trend values of 0.048℃/a and 3.954×10^-4 a^-1, respectively; while the spatially averaged solar downward shortwave radiation significantly decreased at a rate -0.070 W m^-2 a^-1 (P <0.01). (2) The NDVI in 34.0% area of the Qinghai-Tibet Plateau showed a significantly increasing trend, which mainly distributed in most of the northern and western Qinghai-Tibet Plateau; in 9.2% area of the Qinghai-Tibet Plateau, the NDVI showed a significantly decreasing trend, which mainly located in the eastern Qinghai-Tibet Plateau. (3) The variations in mean soil moisture, mean temperature, cumulative precipitation, and mean solar downward shortwave radiation in the growing seasons during 1982-2015 explained 42%, 19%, 10% and 9% of the NDVI variation, respectively. (4) The relative magnitudes of the effects of mean soil moisture, mean temperature, cumulative precipitation, and mean solar downward shortwave radiation showed obvious spatial differences on the dynamics of vegetation growth in the growing seasons on the Qinghai-Tibet Plateau. The increasing temperature is the primary factor for the NDVI changes in the northeastern and central Qinghai-Tibet Plateau (with relative contribution rate above 40%), however, the increases in soil moisture are the main reason for the NDVI changes in the southwestern and southeastern Qinghai-Tibet Plateau (with relative contribution rate above 50%). In general, the rising temperature and its resulting in the increased soil water content through melting cryosphere (snow, ice, glaciers, and frozen soil) are main reasons for the rapid changes in vegetation dynamics on the Qinghai-Tibet Plateau in recent decades.