The third generation of BeiDou navigation satellite system (BDS) is under construction. The Interface Control Document of B1C interoperability signal has been released. This paper focuses on the analysis of B1C signal and its navigation messages features in comparison with GPS L1C and Galileo E1OS. Analysis shows that B1C has been optimized based on full reference to GPS L1C and Galileo E1OS characteristics. B1C interoperates with the GPS L1C and Galileo E1OS through a system of measures such as using the same center frequency and spectrum structure as L1C and E1OS, adopting the design scheme of the data pilot branches, MBOC modulation and hierarchical code structure, employing the similar navigation message structure to L1C and E1OS. At the same time, B1C also has its own unique features, such as employing QMBOC(6,1,4/33) modulation in pilot branch, using 64-ary LDPC encoding scheme in navigation message. Compared with B1I signal, B1C signal has better weak signal tracking performance, shorter initial positioning time.