Abstract: The shortcomings of quadratic polynomial model are analyzed in secular predicting satellite clock error. Based on the gray system theory and changing law of clock error, the gray predicting model is established by making use of a few observation examples. Its result is compared with quadratic polynomial model. Calculating results show that the short-term predicting precision of the two models is almost same, but the gray predicting model remarkably improves the secular predicting accuracy of satellite clock error, so the gray predicting model is fitter to be used in practice.