The reason of making propeller error in grinding square aspheric optical elements is analyzed. Each rigidity index of two fixing methods of abrasion wheel axis is calculated, and then the influence of abrasion wheel axis fixing position on the processing accuracy. The experiment at each position is done. Different abrasion wheel and different processing parameter are used to do the grinding experiment. Finally, the abrasion wheel axis fixing position and the grinding processing parameter which can satisfy the processing accuracy of square aspheric optical element are obtained.