In this paper, several methods are put forward, by which axial resolution of scan microscope could be improved. One is that detecting method of ordinary laser feedback is improved, the orthogonal polarized lights split by Wollaston prism are detected separately, comparing to the ordinary feedback, the axial resolution is improved about 2.9 times. Another is that the orthogonal polarized lights, o-light and e-light, generated by dual frequency laser, is used instead of ordinary feedback light, the axial resolution is improved about 2 times. The last is that o-light or e-light is as the feedback light, the axial resolution is improved about 2.5 times. The experimental results indicate that mode competitive effects of orthogonal polarized lights can effectively improve axial resolution of scan microscope.