Urban expansion and land cover changes driven primarily by human activities have significant influences on urban eco-environment,and together with climatic change jointly affect net primary productivity (NPP). However,quantitative analysis about the impacts of human activities on NPP change isolated from climatic change in the spatiotemporal scale is poorly understood. We took Guangzhou City as study area to estimate the actual NPP (NPPact) and the potential NPP(NPPp) from 2001 to 2013 based on Carnegie Ames Stanford Approach (CASA) model and CHIKUGO model,and calculated the loss of NPP due to land use and land cover change (NPPlulc) from NPPact and NPPp. The impact of human activities on NPP in the process of urban sprawl was quantitatively analyzed and assessed by examining a relative contribution index (RCI) based on NPPp and NPPlulc. Guangzhou City and its five regions showed a declined trend of NPPact and an increased trend of NPPlulc from 2001 to 2013,and significant spatial differences of NPPact and NPPlulc were found in all regions. RCI had an increasing trend over 13 years,the smallest value of average RCI occurred in northeastern region (0.31), indicating climatic change was the main cause of NPP change,while the average RCI was higher than 0.5 in the other four regions,indicating that these regions were subjected to severe anthropogenic disturbances and human activities were the dominant factors of NPP reduction. The slopes of RCI change were positive in Guangzhou and its five regions, revealing an increasing human disturbance trend. Northern region had the largest RCI slope of 0.693,suggesting the trend was most obviously in this region.