In order to further improve the calculation accuracy and reduce the calculation time of the inverse algorithm in the Risley-prism structure, a new algorithm is proposed. It combines the forward iterative method with the equivalent vector model of the Risley-prism to produce an equivalent vector iterative method of calculation. Firstly, the equivalent vector model of the wedge is established according to its deflection. Then, the vector coordinates of the light emitted from the Risley-prism are solved through vector superposition. The equivalent vector model is then substituted into the two-step inverse solution algorithm to calculate the approximate value of the rotation angle of the Risley-prism. Finally, the inverse equivalent vector iteration algorithm is proposed by using forward iteration and gradual approximation, and the rotation angle of Risley-prism is obtained. The experimental results show that the accuracy of the algorithm reaches 10 μm and the calculation time is less than 0.1 ms. The algorithm can effectively improve calculation accuracy, reduce calculation time, and has application prospects in the field of high-precision beam pointing.