Satellite Laser Ranging (SLR) is a very important technical means in geodesy and geodynamics. It is also a very important tool to calibrate the spaceborne altimeter, such as Geos-3, Seasat, Geosat, ERS 1 and 2, TOPEX/Poseidon, and just launched GFO-1, and it is the only way to calibrate the spaceborne altimeter satellite on-orbit. So the precision and accuracy of SLR system will play an important role in determining the measurement accuracy of the altimeter. This paper presents the improvement of range precision and stability laser ranging system in Changchun Artificial Satellite Observatory, the range precision and stability of the satellite laser ranging system have been greatly improved. A high quantum efficiency, low time walk, compensated, low work voltage and fast response time single photon avalanche diode was applied to the system, besides a portable calibration system and three new near ground targets. Now, the system produces subcentimeter single-shot precision and precision for mm level for normal point data. The long term system stability is improved from 4 cm to better than 2 cm, the range bias is less than 6 cm, and the time bias is less than 50 μs.