Abstract: At present, there are some common coordinate transformation systems , such as seven parameter, four parameter, polynomial fitting, and each has its own advantages and scope of application. In thispaper, we design a method of high-precision mutual transformation between city coordinate systems.which calculates the optimal central meridian and reprojection after changing belts, and then performsfour parameter conversion. The experimental results of the transformation between the national coordinatesystem and the local city coordinate system in Kunming show that the accuracy of internal and external coincidence of the transformation method reaches millimetre level, and batch conversion of various format:of data is realized by programing. The method is suitable for the transformation between independent citycoordinate systems or the China Geodetic Coordinate System 2000 ( CGCS2000)

Key words: coordinate transformation: high precision: relatively independent city coordinate system;central meridian, reprojection