In this paper, the FRT (fringe reflection technique) is used for the off-axis aspheric surface measurement during the manufacture stage of the beginning of polish, duo to its advantage of large dynamic range and high sensitivity. The measurement system coordinate and ray trace model are build using the laser tracker, and the calibration results of the camera calibration and screen calibration are introduced into the Zemax model and the ideal screen pixel point position can be got by ray tracing. The measurement of screen pixel point position is obtained by phase-shifting technique. The slope error of the surface is calculated and final results are got by integration. The measurement results of a SiC off-axis mirror obtained by the presented method and the CMM are compared and feasibility is verified. This method can be used to guide the manufacture of off-axis aspheric surface during the beginning of the polish.