Abstract. Purpose: The aim of this study is to research the impact of the liquid injection in hepatic microwave ablation (MWA) by using finite element method (FEM). Methods: We used the finite element method to simulate the MWA without liquid injection, with 0.9% NACL (saline) and with ethanol in turn. At the frequency of 2.45GHz and the duration time of 300s, we set the microwave powers at 40W, 60W and 80W. The volume of the saline and ethanol was 10ml. Results: Compared to the lesion size of the group without liquid injection, the lesion size with saline was larger in the area range from 19.42% to 60.54%, and the ablation with ethanol was larger in area range from 15.66% to 58.69% as the microwave power increasing. Conclusions: MWA with liquid injection can expand the lesion size effectively.