Abstract: Carbon isotope in tree ring is an effective indicator of climate and environmental change. However, few studies have analyzed the indication effect of tree ring carbon isotope on net primary productivity (NPP) of forests. Based on meteorological factors of growing seasons, we analyzed the variation trend and the relationship between the tree ring δ¹³C chronosequence of Korean pine (Pinus koraiensis) and net primary productivity (NPP) of Korean pine in Changbai Mountain. We found that before 1970, the change of Korean pine tree ring δ¹³C and NPP was synchronous, with a highly significant linear positive correlation between them, indicating that tree ring δ¹³C recorded the impacts of climate change on NPP. After 1970, tree ring δ¹³C was negatively correlated with NPP but not statistically significant, meaning that other environmental factors such as severe droughts reduced the sensitivity of tree ring δ¹³C to climate change and the recording of NPP by tree ring δ¹³C. The δ¹³C of the current year was also correlated with the corresponding NPP in the following year, which indicated that the current year’s environmental conditions were of great significance to the growth of Korean pine in the following year. This study showed that tree ring δ¹³C was a good indicator of the NPP of Korean pine in Changbai Mountain and that tree ring δ¹³C had the potential to reconstruct long-term changes of forest NPP in the history.