Null testing is the main measurement for aspheric surface in modern optical testing. In order to improve null testing, a novel measurement which combines compensator and interference is proposed. The principle of the method is that the radius of the first surface of the compensator is chosen to equal the distance between surface and laser point of interference. The reference wavefront reflected from the concentric surface inferred with the wavefront from the aspheric surfaces under test to accomplish the interference null testing. Base on third-order aberration theory, interference null testing system is designed and the residual aberrations are calculated. The wavefront abberation of designed system is better than λ/170 , if the relative aperture is smaller than 1/4.5. By means of theoretic test, this measurement is proved to be available for testing aspheric surface.