Abstract: A novel computer assisted image guided surgery method for liver cancer microwave ablation is proposed. Advanced GPU accelerated visualization technique is used to reconstruct 3D patient anatomy structure from preoperative CT images in realtime. Thermal field simulation technology for percutaneous liver cancer microwave ablation is introduced, including the calculation of the specific absorption rate of microwave energy, the calculation of tissue temperature field using the Pennes bioheat transfer equation and the calculation of the tissue necrosis zone using the Arrhenius equation. Preoperative surgery planning is performed by the surgeon in an interactively way, until the optimal surgery plan is achieved, including the pose of the microwave probe and the microwave working time and power. Intraoperative sonography is used in the guidance of the placing of the probe in patient and postoperative CT is 3D visualized to evaluate the accuracy of the thermal field simulation and the placement of the microwave probe. Extensive experiments have been performed on both porcine liver and patient with liver cancer and the actual necrosis zone are measured in postoperative CT images for patients. The experiment results show that this method is accurate for surgery simluation and could be used in image guided microwave ablation surgery.