With the development of single-point diamond turning technology (SPDT) and polishing technology, the rapid, efficient and low-cost manufacturing of metal mirrors has been realized. However, the test methods of metal mirrors have obvious shortcomings, especially there is no fast and efficient test method for testing convex aspheric metal mirrors. In order to improve the test efficiency of convex aspheric metal mirrors, a non-null stitching method to test convex aspheric metal mirrors was proposed. Combined with engineering examples, a stitching test experiment was carried out on a convex aspheric metal mirror with a diameter of 120 mm, a radius of curvature of the vertex R of 1121.586 mm, and a conic constant K of -2.38. The residual surface shape obtained by stitching RMS=0.016λ(λ=632.8 nm). Compared with the Luphoscan test results, it is verified that the test accuracy of the non-null stitching test method RMS=0.007λ, which shows this test method can achieve rapid and efficient test of convex aspheric metal mirrors.