Abstract: By introducing the theory of belief revision into the classical situation calculus an open situation calculus system named OSC is constructed. OSC can describe the communications and event-handling ability of the agents which classical situation calculus can’ t. OSC preserves the situation fluent result-of（ a , s ） for the actions, and introduces a new situation fluent bel-rev （ , s ） for the communication and event-handling. A novel function mode is designed, which combines the off-line planning and the on-line execution. OSC provides a theoretical solution for the agent oriented technology.