Using the Inter-satellite links(ISLs) to enhance the GNSS’s positioning accuracy and integrity is attracting much more attentions. In order to ensure the autonomous positioning accuracy and stability based on ISLs, a satellite and ground joint positioning mode is presented in this paper, which is constrained by quality grade of position error. Spatial error ellipsoid is applied to calculate parameters and achieve Signal-in-space(SIS) integrity monitoring. To check the accuracy of the mode and performance of monitoring, mixed constellation of Beidou system is simulated to support the analysis and investigate the impact of the high-low ISLs. The orbit determination results verify that the introduced integrity monitoring method can satisfy the integrity risk of 10-5/h and achieve the SIS integrity monitoring. Using the Inter-satellite links (ISLs) to enhance the GNSS’s positioning accuracy and integrity is attracting much more attentions. In order to ensure the autonomous positioning accuracy and stability based on ISLs, a satellite and ground joint positioning mode is presented in this paper, which is constrained by quality grade of position error. Spatial error ellipsoid is applied to calculate parameters and achieve Signal-in-space (SIS) integrity monitoring. To check the accuracy of the mode and performance of monitoring, mixed constellation of Beidou system is simulated to support the analysis and investigate the impact of the high-low ISLs. The orbit determination results verify that the introduced integrity monitoring method can satisfy the integrity risk of 10-5 / h and achieve the SIS integrity monitoring.