Abstract: To study the effect of the wheel-arc error on large-scale rectangular axisymmetric aspheric machining, the grating parallel grinding method is adopted and the mathematical model of wheel-arc error separation is built. The factors that affect the surface accuracy are analyzed and it is found that the wheel-arc error is the most sensitive in the factors. According to the grinding and measurement method, the wheel-arc error is separated. Using the new wheel-arc radius modified by separated wheel-arc error and the new compensation data subtracted from wheel-arc error, the separating error compensation grinding is carried out and proves effective. The experimental results show that the aspheric surface error decreases by 14% and 35% after separating error compensation grinding in rough and fine grinding conditions. The error model can separate the wheel-arc error effectively and the accuracy of the aspheric surface is improved.