Abstract: Based on the fact that GPS and GLONASS measurements contain hardware delay biases,the mathematic model of the combined GPS and GLONASS precise point positioning(PPP) is derived and the influence of the hardware delay on estimated unknown parameters is further analyzed.The existence of the hardware delay biases is validated by results obtained from several IGS stations.The combined GPS/GLONASS PPP model is tested using IGS static data and kinematic data collected from an experiment.The obtained numerical results are analyzed with a comparison to that of GPS-only PPP.