Novel conformal window can enhance the aerodynamic performance of aircraft obviously. Due to the surface complexity of these conformal windows, the measuring of conformal windows is infeasible by using the conventional optical measurement technique. In this paper, we describe a new sub-aperture stitching method for conformal measurement, and introduce the design of this technology. Based on the theory of compensation method, a compensator is designed for a 70mm aperture conformal window, of which the final residual wavefront error(RMS) is 0.0515λ(λ=632.8nm).