Abstract: Objective:To evaluate the application of conformal radiotherapy based on CT simulation in different respira -tory phases for primary liver carcinoma. Methods:A total of56patients with unresectable primary liver carcinoma were treated with conventional fractionated radiotherapy based on CT images in different respiratory phases. Of these 56pa-tients, 44presented with a solitary lesion and 12with multiple ones. Twenty-one cases were initially treated with transcathe -ter arterial chemoembolization (TACE) and then sequentially with radiotherapy. Fourty-nine cases were treated with confor -mal radiotherapy and the principle of the scheme was to protect part of the liver from irradiation. The larger the tumor was, the less fields were used. Seven patients with small lesions were treated with rotated fields. PTV, local efficiency, patient survival and radiation-induced liver disease were analyzed. Results: Compared with the traditional expanding of CTV-PTV, the volumes of PTV in this scheme were averagely 18.7 percent lower. The local response rates (CR+PR) were 94.6% (53/56) at 3 months and83.9% (49/56) at 1 year after treatment. The 1-, 2-, 3-, 4-, and 5-year survival rates were 78.6% , 51.8% ,35.7% ,19.1% and 16.7% , respectively. The median survival duration was 23.5 months. The incidence of radia-tion-induced liver disease was 8.9% (5/56) and was of Child B class. Conclusion:CT simulation in different respiratory phas-es can effectively reduce the PTV and the incidence of radiation-induced liver disease, without affecting the therapeutic ef-fect.