Abstract:Terrestrial net primary productivity (NPP) is an important component of the surface carbon cycle. In order to deeply understand the effects of human activities on terrestrial ecosystem, it is very necessary to evaluate the relative contributions of climatic fluctuation and land cover change to NPP variations. Based on the scenario simulation method, the CASA (Carnegie-Ames-Stanford Approach) model was used to estimate actual vegetation NPP of Guangdong Province in the year 2000, 2005 and 2010. The relative contribution of climate fluctuation and land cover change to vegetation NPP change was also discussed. The results showed that there was significantly positive correlation between solar radiation and NPP and significantly negative correlation between temperature and NPP, precipitation is not a limiting factor in vegetation growth, the correlation between each climate factor with NPP displayed seasonal and regional difference. Under the constant climate conditions, the land cover change caused an overall NPP gains and its relative contribution to NPP variations was similar to the urban expansion pattern. Regional differences existed in the four eco-regions with the largest contribution in the Pearl River Delta. Overall, the relative contribution of climatic fluctuation was more complex, which depended on the fluctuation characteristics of climate factors and their correlations with NPP; other influence factors (urban heat island, agricultural activities, gardens management and so on) existed some uncertainties and increased NPP as a whole.