Based on the Z/X/B triaxial CNC machine, a constant tangent-face angle(CTFA) method for high-order aspherical grinding is proposed. In this method, equal chord length is used as the criterion to dissociate the profile of the aspherical, and the tangent-face angle is assumed as a constant to calculate the running process of CNC machine. The equal chord length criterion can avoid excessively step of the profile dissociation which was caused by the slope gradual change, and CTFA method makes the grinding wheel to finish the grinding process kept using front face edge, which helps to achieve a aspherical surface in high precision and consistency. In addition, the grinding process with CTFA method is simulated by computer programming and the result shows that, parameters δ and C should make the running of CNC machine meets the conditions of no physical collision between the work piece and machine components, no reverse running of CNC machine in treble Z/X/B direction, running step must not smaller than the resolution of CNC machine and to make the process route of the machine as short as possible. The deviation of aspherical surface caused by grinding wheel abrasion can be relieved by reprogramming the CNC process after the working edge was sharpened or take the abrasion edge of the wheel as the working edge.