Abstract: In order to test large aspheric surfaces without the aid of null optics, the subaperture stitching interferometry (SSI) was proposed. The theory and principle of the technique were analyzed, the optimized stitching model and effective stitching algorithm were established based on homogeneous coordinates transformation, simultaneous least-squares method and Zernike polynomials fitting. The software of SSI was designed, and the computer simulation was carried out, the prototype for testing of large asphere by SSI was designed and developed. The experiment was conducted with five subapertures for a 350mm hyperboloid. For comparison and validation, the asphere was tested by null compensation as well, the synthesized surface map is consistent with the entire surface map from the null test; and the difference of PV and RMS error between them was 0.032 and 0.004(=632.8nm), respectively.