Research conclusions: With the precisely determined geoid model，the GPS control network spot is fitted in height and the internal and external accuracies of the precisely determined geoid model are checked and analyzed．The result shows the accuracy of the precisely determined geoid model is better than±3．5 cm．the normal height with centimeter—level accuracy can be got and this really achieves the three—dimensional positioning function of GPS technology in the geometry and physical senses．Compared with the traditional standards of leveling measurement，by using the precisely determined geoid，there is no error accumulation，the labor intensity can be much reduced and the working efficiency Call be improved．Under conditions that the traffic is inconvenient and topographical condition is complicated，the calculation accuracy of the normal height Can reach at centimeter level by using the high—resolution geoid model，which is a big leap in railway level surveying．