Abstract: Using precise ephemeris to solve satellite coordinates is the primary basis for high precision differential positioning of GPS. In order to obtain satellite coordinates at any time since the GPS precise ephemeris has limit of the sampling interval, it is necessary to interpolate and extrapolate GPS precise ephemeris data. After analysis on the regularity of satellite position changing with time, the interpolation and extrapolation model which is relative to time is built by generalized extension method, and it is used to describe a section of satellite orbit, the calculation process of satellite coordinate is simplified without introducing comparatively larger position error through this method, which is then compared with the Lagrange interpolation method in experiment. The result shows that the error of interpolation when using generalized extension method is less than 5cm, and the accuracy of extrapolation maintains 30 minutes, which is significantly better than the Lagrange interpolation method.