Abstract: The Greater Mekong Subregion (GMS) is a region strongly influenced by the East Asian monsoon and characterized by active land-atmosphere interactions, where soil moisture-evapotranspiration coupling plays an important role in regulating regional hydrothermal processes. Significant differences exist among CMIP6 models in their simulation of coupling characteristics over this region. Identifying the dominant modes of these inter-model differences and their possible causes is therefore important for understanding the uncertainty in regional land-atmosphere coupling simulations. Based on historical simulations from 29 CMIP6 models, this study investigates the spatial distribution of the soil moisture-evapotranspiration coupling index (TCI) over the GMS during the dry and wet seasons, as well as its inter-model differences. EOF analysis, regression analysis, and composite analysis are further employed to explore the possible mechanisms underlying these inter-model differences from the perspectives of hydrological and energy processes. The results show that: (1) the first mode of inter-model TCI differences exhibits a regionally coherent pattern, reflecting differences among models in the simulation of the overall coupling strength across the region. During the dry season, this mode is mainly related to hydrological processes, whereas during the wet season it is primarily associated with differences in net radiation flux. (2) The second mode of inter-model TCI differences exhibits a meridional dipole pattern, reflecting differences among models in the simulated spatial structure of land-atmosphere coupling within the region. In the dry season, this mode is mainly associated with the north-south contrast in soil moisture among models, whereas in the wet season it is mainly related to differences in the spatial gradient of net radiation flux within the region.