The rotation method is an absolute testing to obtain rotationally asymmetric surface. A compensation method based on rotation-averaging needs a different rotation measurement besides N equally spaced azimuthal measurements, which is called N+1 rotation method. The losing surface of rotation-averaging method can be obtained with the additional measurement data and Zernike polynomial fitting. The theoretical formulas are derived and the validity of compensation method is simulated. The impact of additional rotation angle on algorithm accuracy is presented. The experimental result is consistent with simulation very well which proves that the losing surface can be compensated effectively by this method with an appropriate angle. Compared with the rotation-averaging method, this method can greatly improve the testing efficiency and accuracy by just adding one additional measurement. The compensation ratio is 0.61 and the accuracy is improved by a factor of 1.