Abstract: The problems on coordinate system conversion and precision of conversion surveying points are always encountered in surveying engineering. For solving the reliability problem of precision of line length between conversion surveying points in practical engineering, on the basis of previous study results and the method of building a plane simulitude conversion model by using least squares estimation, an effective way solving the presision problem of line length between two surveying points in coordinate is theoretically proposed. Througth the result of an illustration calculation and visualization analysis t he reliability of the method is verified theoretically, meanwhile, its practicability and operaling reliability is revealed.