Density functional theory (DFT) is a powerful tool to study heterogeneous catalysis nowadays. In past decades, numerous DFT calculations have been conducted to investigate the mechanism of catalytic reaction from which the rationale of catalyst design can be revealed. Because the catalyst electronic and geometric structures determine the intrinsic activity, corresponding composition, size, and morphology have been explored extensively to tune the structure–activity relationship for higher activity and selectivity. In this review, we focus on the recent theoretical progress of the crystal phase effect on catalysis. Catalysts with different crystal phases have different symmetries, and could expose very different facets with distinct electron...