Abstract: With the expressive power of the software architecture description language C2, a compositional method of specifying and constructing agent is proposed, which is based on three elements of software architecture, such as component, connector and architecture topology. Firstly, the evolution of agent via subtyping is proposed with the aid of type theory of software architecture. Secondly, an expanded relationship is used to represent the relationship among different types of agents. Finally, non agent software entity can be migrated to agent through customizing wrapper, domain translator, interface and constraints for legacy code. Some cases show that these methods, such as composition, evolution via subtyping, expanding and migrating, can satisfy the demand of diversity of types of agents in constructing multi agents systems.