【Objective】An in-depth understanding of how species composition influences the relationship between individual tree height (HT) and diameter at breast height (DBH) in mixed forests is important for effective implementation of forest quality improvements. 【Method】 The functions relating the HT and DBH of individual larch (Larix gmelinii) and birch (Betula platyphylla) were estimated using multiple stepwise regression with tree, stand, and species information extracted from 112 larch-birch mixed forests in the central part of Greater Khingan Mountains. The effects of the different variables on the relationship between HT and DBH were quantified using hierarchical partitioning. Finally, mixed-effects modelling techniques were employed to characterize nesting effects and solve heteroscedasticity problems within the sample survey data. 【Result】 The correlations between HT and DBH of the main tree species in Greater Khingan Mountains were affected simultaneously by the DBHs of the individual trees, stand characteristics (i.e., HT of dominant tree, as well as mean DBH and HT of the stand), and species composition (i.e., the volume percentage of larch and birch). The individual contributions on the HT-DBH relations from the various variables were as follows: DBH of individual tree (82%) > stand characteristics (16%) > species composition (2%). Furthermore, the mixed-effect models of HT-DBH were each optimally combined with three random parameters, as well as variance covariances with pdSymm structure and heteroscedasticity correction with varPower functions, in which the values of R_adj both increased by about 2.50% and 3.44% (0.789 5 of larch and 0.744 7 of birch) when compared with that of the basic model. 【Conclusion】 From the perspective of forest management practices, individual tree HT growth can be promoted by adjusting the species composition of forests through suitable cutting or replanting.