Thesimilaritytransformationmodelbetweendifferentcoordinatesystemsisnotaccurateenoughtodescribethediscrepancyofthem.Therefore,thecoordinatetransformationfromthecoordinateframewithpooraccuracytothatwithhighaccuracycannotguaranteeahighprecisionoftransformation.Inthispaper,acombinedmethodofsimilaritytransformationandregressiveapproximatingispresented.Thelocalerroraccumulationanddistortionaretakenintoconsiderationandtheprecisionofcoordinatesystemisimprovedbyusingtherecommendedmethod.