Abstract: In this paper the problems of the national geodetic coordinate system are pointed out in terms of advanced character and practicability,the choices of the coordinate systems are put forward and the adoption of a geocentric coordinate system are proposed.Then the opinions are given on the definition and realization of geocentric coordinate system,the constants of reference ellipsoid and the normal gravity formulas.Finally the influence of the change of coordinate system upon the old topographic maps is studied.The main conclusions are drawn as follows:the existing national coordinate systems have failure of their advanced character;they have increasingly failed to fit in with the needs of national economic construction and national defence construction and with the development of space technology;the geocentric coordinate system can fulfill the scientific and practical demands of the geodesy,aerospace science and technology,geoscience study,navigation etc.;the national coordinate system should be updated to the geocentric from the local system;the definition of the national geodetic coordinate system should be consistent with IERS conventions;the adopted ellipsoid and normal gravity formulas should be in common use internationally.The proposed ellipsoid and the formulas conform to these principles.Furthermore the proposed scheme of the old topographical map correction for the change of coordinate system should be basically feasible and practical.