Object-Oriented technology is fit for the construction of open systems. However, how to express distributed or concurrent objects has not been resolved in nowadays OO language. The active object concept is one kind of generalization of concurrent or distributed objects. We analyzed the characters of active objects in detail and propose an efficient method to express active behaviors in Object-Oriented language such as C++. What we lay stress on is to express active objects' two major features: concurrency and cooperative, especially the latter. The reusability of active objects is emphasized as well.