Multispectral zinc sulfide is widely used in infrared optical guidance seeker， photoelectric detection radar and airborne photoelectric pod because of its high optical transmittance in near， middle and far infrared spectral bands. In order to obtain multi-spectral ZnS optical element with ultra-high surface shape accuracy and improve ion beam polishing efficiency， the orthogonal experiment method was used to carry out ion beam single point etching experiments on ZnS， and the removal function characteristics and volume removal efficiency were obtained under each process parameter. Through direct analysis of orthogonal experimental data and range analysis， the process parameters were optimized with the target of maximum volume removal rate. The optimized process parameters were obtained as follows： ion beam voltage 1 100 V， radio frequency power 110 W， acceleration voltage 200 V， argon flow rate 7 sccm， and processing distance 30 mm. By adjusting the process parameters， different ion beam spot diameters were obtained for combined polishing of 80 mm diameter zinc sulfide. After processing， the surface shape accuracy of zinc sulfide decreased from 467 nm to 71.506 nm and from 112 nm to 10.75 nm. The above experimental results show that the combination of large and small diameter ion beams can effectively improve the processing efficiency and surface shape accuracy of multi-spectral ZnS optical elements.