A dwell time algorithm for the magnetorheological finishing (MRF) of the small axis-symmetrical aspherical surfaces is described. The dwell time at each dwell grid is calculated as integer multiple of the workpiece rotation period. The removal rate on the surface of workpiece is transferred to a removal matrix. Nonnegative least-squares solution is used to obtain the optimal solution of the dwell time. A piece of axis-symmetrical aspherical surface glass is polished on the MRF experimental facility developed by us. After iterative polishing three times, the residual error of the workpiece decreases from 8μm to 0.5μm.