The fundamental principle and considered fundamental factors of GPS precise point positioning are discussed, the experimental research show that the error of GPS precise point positioning is greater to use broadcast ephemeris, and broadcast ephemeris can obtain only the accuracy of meter level, the positioning error of Z direction is greater than X direction and Y direction to use IGS precise ephemeris to do GPS precise point positioning, the positioning accuracy has not obvious difference to use ultra-rapid ephemeris in different time to do GPS precise point positioning, and the positioning accuracy has not obvious difference to use rapid ephemeris and final ephemeris to do GPS precise point positioning, the arrangement of the accuracy from high to low is final ephemeris, rapid ephemeris, ultra-rapid ephemeris, broadcast ephemeris to three dimensional positioning, it is not necessary to prolong the observation time unlimitedly to raise the accuracy of GPS precise point positioning, the positioning error and the positioning standard deviation have the similar tendency, but they exist obvious difference, the positioning accuracy to use IGS final ephemeris to do GPS precise point positioning can obtain the level of centimeter.