Abstract: With the data of BDS, GPS, Galileo and GLONASS of ten stations in MGEX in January 2018, the ionosphere-free model and the un-differenced and uncombined model are used to analyze the positioning performance of PPP in single-system, dual-system and four-system. The positioning performance analyzed in this paper includes convergence time and positioning accuracy. The experimental results show that the positioning performance of the two PPP models is equivalent, and they are better than the single-frequency PPP. The convergence time in the E, N, and U directions is shortened at about 20 minutes, and the positioning accuracy is improved at about 1.6 cm. Multi-GNSS can increase number of satellites, and improve inter-satellite geometry and  positioning performance of PPP. The GLONASS pseudorange IFB is estimated to use the pseudorange IFB model and the pseudorange IFB of each GLONASS satellite as the frequency quadratic polynomial model. The results show that the pseudorange IFB model of each GLONASS satellite is better than the pseudorange IFB for the frequency quadratic polynomial model. The two model of pseudorange IFB estimation have certain degree of improvement in PPP positioning performance compared to that ignoring the pseudorange IFB.