Coordinate transformation (C-T) is an important link in the formation processing of air-defense C3I. The transformation from spherical surface coordinate of radar's station to right-angle coordinates of the command center is fulfilled through the earth-centered coordinates, which makes the conversion to the location directly, overcomes the error maybe produced from the processing of C-T. The detailed derivation process and transformation method are given out Considering the effects of the curvature of the earth's surface, the analysis and compensation for the errors are carried through and several methods for the error estimating are brought out.