Human Activity Intensity (HAI) is an objective indicator that characterizes the degree to human activities which affect the natural environment. Vegetation, as a comprehensive indicator of ecological environment changes, is very sensitive to changes in human activities. Deeply exploring the spatio-temporal differentiation and correlation between HAI and Normalized Difference Vegetation Index (NDVI) is of great significance for maintaining stable natural environment, reasonably controlling human activities, and coordinating human land relations. Taking the Loess Plateau as a representative region, based on nighttime lighting, population density, and land use data to characterize human activity intensity, this study analyzed the spatio-temporal differentiation of HAI and NDVI from 2000 to 2020, and further analyzed the spatio-temporal correlation between the two. The results showed that: (1) From 2000 to 2020, the overall change of HAI on the Loess Plateau was relatively slow (with an average annual rate of 1.39%), and the spatial distribution pattern showed a "seven point one circle" pattern. The intensity of HAI in the Hubao Eyu and Jinzhong urban agglomerations changed more frequently, and the high-intensity areas showed a concentrated distribution trend towards the northwest. (2) In the early stage (2000-2013), when the NDVI was vigorously carried out, the growth rate was relatively fast (2.11%/a), and in the later stage (2014-2020), the growth rate slowed to 0.82%. The overall distribution of NDVI was high in the southeast and low in the northwest. The high vegetation coverage area moved to the northwest and expanded in many directions. (3) The correlation between the HAI and NDVI showed significantly spatial differentiation, and a spatial clustering distribution in the Guanzhong, Hubao, and Jinzhong urban agglomerations. The effect of human activities on vegetation cover had a bidirectional nature. High intensity human activities have led to a sharp reduction in vegetation coverage. Restoration projects such as Grain for Green and grasslands, and land reclamation and afforestation could effectively curb vegetation degradation and improve the ecological environment. The results can provide a theoretical basis and reference for the precise quantification of human activity intensity, future land spatial planning, ecological environment restoration and stability maintenance of the Loess Plateau.