Study of the sub-surface damage induced by chemical-mechanical polishing method has been carried out for HgCdTe material. The optical characterization was performed for the surface after repeated step removal by wet etching using spectroscopic ellipsometry. It was found that the depth of sub-surface damage layer was about 15-20 times of the diameter of the abrasive particles. Through the comparison of the minority carrier lifetime and performance of the ultimate photoconductive detectors, it was considered that an obvious improvement could be achieved by a complete removal of this sub-surface damage layer.