Solvent-assisted steam-gravity drainage (SA-SAGD) has lately been viewed as one of the most efficient alternatives to develop heavy oil reservoirs. However, there is strong evidence that reservoir heterogeneity along the horizontal well can significantly affect chamber evolution and energy efficiency which has been rarely investigated for SA-SAGD. In this study, a mathematical method is proposed for the chamber growth in the heterogeneous reservoir by considering the wellbore flow effect coupled with the effect of phase change. Subsequently, the recovery rate and the energy efficiency, defined as the steam-oil ratio (SOR) of SA-SAGD, under different permeability distributions along the horizontal well are estimated using the method. The results reveal that heterogeneous reservoirs with high-to-low permeability distribution can achieve the highest oil production from SA-SAGD, but they are still lower than those in the homogeneous reservoirs. In addition, the highest energy efficiency in the SA-SAGD project can be achieved by injecting hot fluid from the lower permeability to the higher permeability region in the heterogeneous reservoir. The findings of this paper shed light on understanding the effects of reservoir heterogeneity along the horizontal well on the SA-SAGD project evaluation and the optimal designing for the decision of the injection direction in the SA-SAGD project, which can be applied to more reliably investigate greenhouse gas emission and economic benefits in a future bitumen exploitation project.