•Species mixing improved the water absorption of Pinus massoniana from shallow soils.•Species mixing reduced the water uptake proportion of P. massoniana from deep soils.•Plant rather than soil properties mainly regulated P. massoniana water uptake in well-watered conditions. Tree species mixtures have been identified as an effective strategy to cope with global climate change. Global climate change not only triggers extreme drought, but also stimulates extreme precipitation, resulting in frequent floods and subsequent tree mortality. However, previous studies concentrated primarily on the response of mixed species to extreme drought, with limited studies involving their response to extreme precipitation, especially at the regional scale. Here, we used δD and δ18O coupled with the MixSIAR model to analyze the water use pattern of Pinus massoniana between pure and mixed stands following different magnitudes of rainfall events across southern, central, and northern subtropical China. We further employed partial correlation analysis, variation partitioning analysis and a random forest model to discern the dominant factor affecting plant water absorption. Our results indicated that the proportion of water uptake by P. massoniana from the 0–40 cm soil layers in the mixed stand was significantly higher than that in the pure stand (56.5–81.4 % vs. 44.3–61.7 %), while the proportion of water uptake from the 60–100 cm soil layers exhibited the opposite pattern (9.0–25.0 % vs. 24.1–32.2 %), whether in light, moderate or heavy precipitation. Furthermore, our results revealed that the difference in P. massoniana water absorption between pure and mixed stands was mainly due to the shifts in plant attributes (i.e., root biomass, leaf biomass and predawn leaf water potential). These findings imply that mixed tree species distributions could optimize water uptake patterns by altering plant properties for interspecific niche complementarity, which could effectively increase forest water conservation.