As important manifestations of ecosystem function, clarifying the relationships among regional net primary productivity (NPP), climate change, and human activities is an urgent topic to explore in the context of global climate change and the "dual-carbon" strategy. On the basis of Moderate Resolution Imaging Spectroradiometer (MODIS) NPP data and meteorological and land cover data, we quantitatively investigated the spatial and temporal changes in NPP in different vegetated ecosystems in Guizhou Province and their responses to the driving factors via Theil–Sen trend, multiple linear regression, and correlation analyses. The results revealed that (1) spatially, the area of Guizhou Province where NPP showed an increasing trend accounted for 51.44%, which was much larger than the area where the decreasing trend accounted for 6.42%. Temporally, the NPP in Guizhou Province showed a fluctuating increasing trend, with a rate of 3.65 gC/(m2·a). Under the influence of climate change and human activities, the NPP of all ecosystems showed a fluctuating increasing trend, among which the grassland ecosystem presented the most significant increasing trend in NPP, with a rate of 5.91 gC/(m2·a). (2) Climate change has had a dual effect on NPP in Guizhou Province, but the overall effect has been one of facilitation. Among the factors, temperature and precipitation were positively correlated with NPP at percentages of 82.83% and 72.8%, respectively, with a greater facilitating effect than an inhibitory effect. Sunshine hours and relative humidity were negatively correlated with NPP, accounting for 67.9% and 53.39% of the area, respectively, and the inhibitory effect was slightly greater than the promotional effect. Among the ecosystems in Guizhou, farmland ecosystems were the most significantly affected by climate change. (3) Human activities played a dual role in NPP in Guizhou, but their overall role was that of facilitation. The transformation of forestland and cropland was the main factor influencing the increase in NPP. Among the ecosystems in Guizhou, grassland ecosystems were the most significantly affected by human activities.