Global climate change has caused changes in the structure and function of forest ecosystems, and even tree mortality and forest decline. Studying the response of forest growth to climate change, especially to extremely drought events, will help predict the stability of the ecosystem under future climate change. In this study, five Mongolian pine (pinus sylvestris var. mongolica) plantations of different ages were selected in Zhanggutai town, Liaoning Province. We analyzed the response of radial growth of trees to climate factors and groundwater level dynamics. The results showed that the autumn temperature, especially the minimum temperature, significantly affected the growth of Mongolian pine forests (except the 44-year-old stand); The growth of Mongolian pine forest with lower ages (i.e., 36 and 39 years) was significantly positively correlated with the precipitation in current summer or growing season, while that with greater ages (i.e., 52 years) was significantly positively correlated to the precipitation in current spring, especially in current February and current May; The chronologies of 36, 39 and 52 year-old Mongolian pine forests were significantly positively correlated to Palmer Drought Severity Index (PDSI) in current summer, while the chronologies of 44 and 58 year-old stands were significantly negatively correlated to groundwater level. In response to the early drought event occurred in 1997, the growth resistance of Mongolian pine increased with increasing stand age, while the recovery decreased. In the subsequent two drought events, the resistance of Mongolian pine forests with greater age was no longer significantly higher than that with lower age. It might due to the obvious decrease in groundwater level, which affected root the water absorption. Affected by cumulative drought, the resilience of Mongolian pine plantations with five ages to the 2007-2008 drought event was less than 1, and the radial growth was significantly reduced. Groundwater level is an important factor affecting the growth and drought resistance of Mongolian pine plantations at different ages. Considering the effect of groundwater level can further improve the accuracy of research on forest ecosystem response to climate change.