To achieve high-efficiency and low-defect machining of fused silica optics， the material removal characteristics and surface quality formation mechanism based on magnetically assisted polishing technology were studied. Magnetic polishing fluid with different degrees of polishing clearance and different volume ratios of iron powders was used to conduct magnetically assisted polishing of lapped fused silica optics. The material removal rate， profile of polished spots， surface roughness， and transmittance of samples were evaluated， and the effects of the processing parameters on processing efficiency and surface quality were determined by combining a spatial magnetic flux intensity simulation and polishing pressure analysis. Results show that the material depth removal rate increases as a power function with the magnetic flux intensity and rises significantly with the volume ratio of iron powders in the polishing fluid. In addition， polishing fluid with a low spatial magnetic field intensity and low volume ratio of iron powders can facilitate material removal in the elastic domain， resulting in a smooth surface. A small polishing clearance of 0.5 mm and high iron powder volume ratio of 14.18% in the polishing fluid can obtain maximum depth removal and volume removal rates of 0.439 2 μm/min and 1.49 × 10^-4 mm³/min， respectively. A large polishing gap of 1.5 mm and a low volume ratio of iron powders of 9.93% generates a smooth surface with R_a roughness as low as 8.1 nm.