The absolute testing method is an effective way to remove system errors of interferometer and improve the accuracy of the measurements of surface deviation. The method of single rotation based on least-squares fitting of Zernike polynomials requires rotating the spherical surface once and taking two measurements to calculate the rotationally asymmetric surface deviation. The formulas are derived theoretically in detail and the analysis of the impact of angle of single rotation on algorithm accuracy is presented. To prove the effectiveness of the method, the experimental result obtained from this method is compared with that of the multi-rotation method, and they meet well.