Based on simulations by the Beijing Climate Center climate system model version 2 (BCC-CSM2), the possible changes in net primary productivity (NPP) of the terrestrial ecosystem in China during the 21st century are explored under the Shared Socioeconomic Pathway 2 (SSP2) 4.5 scenario. We found both the near-term and long-term terrestrial NPP basically shows a unanimously increasing trend, which indicates low ecosystem productivity risk in the future. However, the simple linear regression is insufficient to characterize the long-term variation of NPP. Using the piecewise linear regression approach, we identify a decreasing trend of NPP in large areas for the latter part of the 21st century. In the northeast region (NER) from east Inner Mongolia to west Heilongjiang province, NPP decreases significantly after 2059 at a rate of -0.9% dec-1. In the south region (SR) from Zhejiang to Guangxi provinces, a rapid decline of -2.4% dec-1 is detected after 2085. Further analysis reveals that the rapid decline in SR is primarily attributed to the decrease in precipitation, with temperature playing a secondary role, while the NPP decline in NER seems to have no evident relations with climate change. These findings are useful for making preparations for potential ecosystem crisis in China in the future.