Abstract: In order to improve service performance of navigation constellation,many experts consider the mixed constellation configuration of GEO satellite,IGSO satellite and MEO satellite.In the design of the new constellation configuration or the research of the existing constellation performance,the inter-satellite link(ISL) is needed to established,and the connectivity and robustness of the ISL are needed to analyze.The characteristics of the mixed constellation configuration are analyzed,and the characteristics of ISL establishment and the service performance of GEO satellite,IGSO satellite and Walker-δ constellation are discussed firstly.Then,the method to determine ISL connectivity in the mixed constellation by the adjacency matrix is put forward,and the standards of the ISL robustness are given using the number of ways between any two satellites,cutting point,cutting edge,k-connectivity degree and k-edge connectivity degree of graph theory.The minimum required number of ISLs of a k-connectivity′s constellation and the construction method of k-connectivity′s constellation are given for the first time.Finally,the 3GEO+3IGSO+24MEO constellation configuration is simulated.The criteria for ISL establishment,the connectivity and robustness of this mixed constellation configuration are studied,and many important conclusions are obtained.