Cyber-Physical System (CPS) tightly integrates control software and embedded components, incorporating software with control domains. CPSs are pervasive and often mission-critical, therefore, they must have high level of security. With the extensive use of information technology, embedded control software plays a greater role in such systems. The close interactions between control software and embedded components demand co-verification. In this paper, an automata-theoretic approach is presented to co-verification. Co-verification, which verifies control software and embedded components together, is essential to establish the correctness of a complete system. The foundation of this approach is a unified model for co-verification and reachability analysis of the model. The LTL formula is converted into a Büchi automata, which is interleaved with the execution of the unified model under analysis. An online-capture offline-replay approach is proposed to improve the usefulness for formal verification. Case studies on a suite of realistic examples show that the presented approach has major potential in verifying system level properties, therefore improving the high-assurance of system.