In order to measure the off-axis aspheric surface before optical testing, method of using a laser tracker to measure the surface shape is investigated. The procedure and data processing method of the measurement are introduced. Using a commercial laser tracker, an off-axis parabolic mirror with an aperture of 150 mm, radius of curvature of 1200 mm, and off-axis distance of 240 mm is measured. The measurement uncertainty is analyzed and measurement result is compared with that of coordinate measuring machine. The result shows a peak-to-valley value consistency better than 1 μm. The method is easy operation and flexible, and meets the measurement requirements of the off-axis aspheric mirror surface before polishing.