Abstract: Below-ground competition in mixed stands is an important breakthrough point for revealing species configurations, competitive strategies, and coexistence mechanisms in plant communities, however the existing research lacks a quantitative analysis of the extent of this competition. In this study, we used the PS index and Levins' overlap index, combined with stable isotope technique, to quantitatively analyze competition between water sources and root systems in typical forest stands of Michelia maudiae × Liquidambar formosana and Michelia maudiae×Chamaecyparis obtusa mixed forests in the mountainous area of southwestern Zhejiang. The study results showed that in M×L, Michelia mainly had absorbed soil water from 80-100 cm (67.2%), while Liquidambar evenly had absorbed soil water from all layers. In M×C, Michelia mainly had absorbed soil water from 80-100 cm (83.9%), whereas Obtusa mainly had absorbed soil water from 0~20 cm (38.3%). The M×L had higher water competition indices (0.95 and 0.84) than M×C (0.68 and 0.60) in the 0-20 and 80-100 cm soil layers. Meanwhile, the root index had indicated that the roots which were in deep soil and farther from the trunk of M×L were more competitive and these roots which were in shallow soil and close to the trunk of M×C were of more comparative advantage. In the mountainous area of southwestern Zhejiang, a hybridization pattern of Michelia and Obtusa is preferred. This study provides a reference for choosing the afforestation pattern for Michelia, a common species in subtropical forests, and for selecting afforestation tree species.