Tangential effusion cooling of a combustor liner has a large difference from traditional effusion cooling on a plate. In this paper, numerical simulation is carried out to study the flow field, heat transfer characteristics and the factors affecting the cooling effectiveness of tangential effusion cooling of a combustor liner. It is found that the cooling film formed by the tangential jet is distributed in a divergent “horsetail” shape and adheres tightly to the inner wall of the liner, which increases the cooling area and effectiveness. Three different tangential inlet cooling hole arrangements and their cooling efficiencies are studied, and several important parameters that affect the cooling effectiveness are summarized. Then, an improved cooling hole arrangement is proposed, and its cooling efficiency is studied and compared with those of the original three arrangements. The results show that the new arrangement significantly improves the comprehensive cooling efficiency and decreases the wall temperature, thus confirming the effectiveness of the improved strategy and providing a theoretical basis for the subsequent cooling design to improve the cooling efficiency for a combustor liner.