Vegetation net primary productivity (NPP) is an important indicator for studying material and energy flows in terrestrial ecosystems. The spatial distribution of NPP is closely related to factors such as regional climate, vegetation growth, and human activities. Its changes can reflect the productivity of vegetation communities and arean important characterization of the function and structure change of ecosystem. In the past two decades, vegetation NPP in the Southwest China has shown an increasing trend. However, it is still unclear about the temporal and spatial patterns of the NPP and the underlying reasons. Therefore, this paper uses MODIS-NPP, lithology, climate, land use, afforestation area, and rocky desertification control data from 2001 to 2018 to analyze the spatiotemporal trends and causes of vegetation NPP in the Southwest China. The results found that:(1) during 2001-2018, vegetation NPP in the Southwest China showed an overall increasing trend. The results of mann-kendall test indicated that the growth rate of NPP (5.13 gC m^-2a^-1) during 2012-2018 was faster than that in 2001-2011 (1.78 gC m^-2a^-1). During 2001-2011 and 2012-2018 the growth rate of NPP in karst areas was higher than that in non-karst areas; (2) The correlation analysis results of vegetation NPP changes and climatic factors in the Southwest China showed that the correlation between NPP changes and temperature(R=0.19,0.26) is higher than that between NPP changes and precipitation(R=0.07,0.05) in both the period of 2001-2011 and 2012-2018, indicating that vegetation NPP in the Southwest China is more susceptible to temperature;(3) The changes of the total amount of NPP under land use changes in 2001-2011 and 2012-2018 showed that the increase in urban land area during 2001-2011 caused the total amount of NPP to decrease, while the area of unused land increase in 2012-2018 resulted in the decrease of the total amount of NPP; (4) The cumulative afforestation area in the Southwest China from 2001 to 2018 was significantly positively correlated with NPP (R=0.7, P<0.05), indicating that the implementation of the"Grain for Green Project" promoted the growth of NPP in the Southwest China. The statistical results show that the rocky desertification area has decreased significantly after 2011, which is consistent with the mutation point of NPP, indicating that the control of rocky desertification plays an important role in the growth of NPP in the Southwest China.