The measurement of aspheric surfaces is very difficult and challenging. An optical system with a single coated lens is proposed for measuring large-aperture aspheric convex/concave surfaces. In this system, the first surface of the compensator is used as an auto-collimation surface, which can realize high-precision null compensation. Based on the third-order aberration theory, the initial design parameters of the system are obtained by analytical calculation, and the parameters are then optimized numerically. An oblate spheroid with an equivalent aperture of 426 mm is taken as an example, and the measuring accuracy of the proposed method can achieve 0.0063λ rms.