The algorithm and implementation of Magnetorheological Finishing with spiral scan mode was researched. The algorithm implemented changes the removal function matrix to the coefficient matrices of the linear system of equations for dwell-time calculation. These equations are resolved quickly because the coefficient matrices are sparse. The variations of speed on the spiral path are obtained by the allocation of the dwell time and the work piece can be processed well using the machine that contains the information about the MRF process. An experiment on a K9 circular plane mirror is made on the KDMRF-200 machine developed by us. The RMS surface error is 0.02λ(λ=632.8nm) through the 2nd iteration.