The processing inspection of large-relative off-axis convex parabolic mirrors is one of the important challenges in optical processing inspection. Combined with a large relative aperture off-axis convex parabolic lens with a diameter of φ100 mm, an off-axis amount of 87.5 mm, and a radius of curvature of 500 mm, the grinding amount of the master mirror is calculated, and a detection method combining the process spherical compensation detection and off-axis Hindle ball detection is proposed. The new method effectively avoids the shortcomings of using either of the two traditional detection methods alone, not only saves processing costs, but also improves the detection accuracy. The precision root mean square (RMS) of the large-relative off-axis convex parabolic mirror processed at last is better than λ/40(λ=632.8 nm), which shows that this method is feasible and can be widely used in practical production and processing.