To investigate the effects of climate changes on carbon-water balances at basin scale in the mountain region of southwestern China, the Biophysical/Dynamic Vegetation Model SSiB4/TRIFFID is coupled with TOPMODEL. Long-term dynamic simulations are run of vegetation succession and carbon-water balances under different climate scenarios for the sub-alpine. The results showed that evapotranspiration of the basin increased and reached its maximal value and runoff reached the minimum during the period of C3 grass succession into shrub. The evapotranspiration decreased, and runoff increased during the period of shrub succession into forest. A temperature increase of 5 ℃ accompanied by an increase in precipitation of 40% [T+5, (1+40%) P] could reduce runoff from forest owing to a significant increase in water loss through canopy interception evaporation and transpiration. Among the three vegetation types forest evapotranspiration increased most, which resulted in forest-runoff relationship changed with variance in temperature. From the control test to the T+5, (1+40%)P test, the forest evapotranspiration increased from 249.7 mm·a~(-1) to 802.9 mm·a~(-1) while runoff depth decreased from 298.0 mm·a~(-1) to 157.9 mm·a~(-1) and the runoff coefficient decreased from 0.43 to 0.16. The net primary productivity increased from 1 025.5 g·m~(-2)·a~(-1) to 1 199.5 g·m~(-2)·a~(-1), while net ecosystem productivity NEP increased from 476.8 g·m~(-2)·a~(-1) to 650.8 g·m~(-2)·a~(-1). As the rate of evapotranspiration was higher than both the net primary productivity and net ecosystem productivity, the water use efficiency (WUE) which characterized the coupling relationship between carbon and water decreased with increasing temperature. WUE decreased and the role of forests to increase runoff changed to reduce runoff with altitude. The vertical zonality of climate controls the spatial variation of the forest-runoff relationship and WUE.