Profile measurement plays an important role in aspherical mirror testing. However, the coordinate deflection and shift will lead to errors in result. In this paper, the analytical mathematic formula for misalignment error is presented. The measurement results are optimized by numerical differentiation method and nonlinear optimization algorithm based on least square method and the influence of these errors is eliminated. This method can effectively reconstruct the off-axis aspherical surface with systematic error. After four times polishing of the 570 mm off-axis aspherical mirror, the surface PV and RMS are decreased from 34.80 μm to 13.83 μm, and from 3.28 μm to 1.89 μm, respectively. For further comparison, the 220 mm×96 mm off-axis rectangle-shaped mirror is measured and proved that this method has strong applicability and generality for special shape mirror.