This　paper　proposed　a　design　of　algorithm　of　an　excimer　laser　coaxial　observation　processing　system　which　can　automatically　track　preset　line.　With　using　of　the　Visual　C　+　+　image　processing　technology　and　the　least　square　method,　the　XY　axis　in　both　directions　of　processing　platform　can　obtain　accurate　processing　displacement,　and　stability　control　platform　for　real-time　tracking　a　straight　line　center.　Processing　system　can　acquire　the　coordinate　of　processing　place　where　can　get　the　distance　from　the　centre　of　image　in　order　to　achieve　real-time　tracking.