In recent years, the United States has successfully launched several new generation GPS III satellites. The observations quality of satellites directly affects the stability, availability and accuracy of the system positioning service, so it’s very meaningful to evaluate and analyze the quality of GPS III satellite observation data. In this paper, the data quality of GPS III and GPS II satellites were analyzed and compared in terms of signal-to-noise ratio(SNR), data integrity rate, multipath effect and observation noise with the observations of 6 MGEX stations. The result shows: The SNR, pseudo-range multipath, and pseudo-range observation noise of GPS II and GPS III satellites are at the same level; The data integrity rate of GPS III satellites in each frequency band is very stable, and the carrier phase observations have a good consistency.