A dwell time algorithm for magnetorheological finishing (MRF) process of optics is developed in this paper. Firstly, the vector of residual heights of the control nodes is calculated, and the removal rate of the “polishing spot” at each control node is written into a removal matrix. Then, a nonnegative least-squares method is used to obtain the optimal solution of the dwell time. With this algorithm, a spherical surface (145mm aperture) is polished on the MRF machine developed by ourselves. After two iterations, PV values λ/15, RMS values λ/125, and Ra ，0.57nm.