Abstract: The using of GPS (Global Positioning System) in space orbit solution is dicussed, especially in the application of HEO (Highly Eccentric Orbit) and GEO (Geodetic Earth Orbit). Aiming at the disadvantage factors of the shortage of visible emitter and weak GPS signal in the HEO and GEO, an efficient algorithm is developed for the acquisition of weak GPS C/A signals. The signals with very low signal-to-noise ratios can be successfully acquired. The capture ability of GPS receive is greatly enhanced that can capture the signal with SNR of 25 dB using the method introduced in this paper. At the same time an original technique based on pseudo-acceleration measurement to compute the fix solution with the spaceborne receiver is presented. The pseudo-acceleration measurements can be computed by pseudorange difference, and the relation between the position and the acceleration can be obtained by Newton's law. When only two transmitters are visible in HEO or only one transmitters is visible in GEO, the state of the receiver (position, velocity, clock bias, and drift) can be obtained. A simulation illustrates that the error is within 100 m in the orbit of 4000 km high and within 2 km in the height of 36 000 km. The simulation result shows that the method in this paper is effective.