Abstract: The relativistic effects on point-positioning precision in the GPS are studied with reference to an earth centered inertial coordinate system. First, the metric coefficient 900 in the earth centered inertial system is obtained from the sun s Schwarzschild isotropic metric, with the gravitation of the earth and the moon taken into account. Then the general and special relativistic effects on the GPS atomic frequency standards, the GPS satellites orbits and the propagation of the GPS navigation signals are estimated, based on which the point-positioning errors caused by the gravitation of the earth, the moon and the sun are evaluated, and the sources and importance of each components of the errors are analysed.