We performed the computer simulation of cathode ablation for a trial fibrillation based on the standard and improved Cox maze III procedure with transmural ablation or not. At first, a computational a trial model was built from MRI images of a male volunteer, and was discretized into spherical units in a spherical coordinate. Then, the anisotropy of conduction velocity and electrical conductivity were incorporated into the special conduction system of this model. The action potential of each cell was simulated based on the Nygren cell model. Furthermore, action potential and conduction velocity restitutions were also introduced to the model. The simulation results demonstrated that non-transmural maze III ablation procedure can achieve the same effect as the transmural ablation if the positions of ablation lines are reasonable. This study may provide theoretical hints and evidence for the usefulness of maze III ablation procedure in the treatment of chronic a trial fibrillation.