Abstract: Objectives:  it is suggested that the multi-frequency GNSS technologies powerfully accelerate the development of high-performance location services. However, the information of multi-frequency and all-system GNSS observations is not fully used in the processing of positioning parameters. Due to that the fixed combination model used in the traditional GNSS PPP solution, the multi-frequency observations are ignored in the parameters estimation. In this research, A GNSS system- and frequency-wide integrated multipath mitigation and positioning model is used to improve the PPP performances.   Methods:  firstly, a code multipath delay estimation model is designed by the combination of the multi-frequency observations in the stage of observations preprocessing, where the impacts of observation noise and ionospheric error are eliminated. Secondly, the multi-frequency ionosphere-free combination is constructed in each system based on the GNSS observations of whole systems and all frequencies to fully model the multi-frequency observations of the users received. Thirdly, integrated GNSS multi-system observations, the mathematical model of all-system and all-frequency combined positioning solution is constructed.   Results:  according to the experiments of GNSS static and kinematics observations, it is indicated that:GNSS multi-frequency observations can quickly mitigate the code multipath delays, especially in the kinematics conditions, where the advantages of multi-frequency observations are significantly presented. In the kinematics positioning solutions, compared with traditional BDS-3 dual-frequency kinematics PPP, the E, N and U directions can be improved with 81.3%, 16.7% and 79.0%, respectively, by the GNSS multi-frequency combined strategy. Moreover, the convergence time is significantly shortened.   Conclusions:  therefore, it is meaningful to use the proposed multi-GNSS and multi-frequency PPP solution, which can promote the improvement of GNSS location services.