Component based software engineering (CBSE) is one of the most effective solutions to improve software development quality and productivity. Component composition and compositional reasoning are the core technologies and frontier research areas in CBSE. Based on the characteristics of software components and inspired by process construction methods in process algebra, in this paper, six component composition mechanisms are proposed to integrate software components simply and conveniently. And it is argued to compose interfaces at the same time of component composition, consequently to generate more powerful and more abstract interfaces to support integration of coarse-grained components and raise the abstract level of component composition. Moreover, based on the Wright’s research on formal specification of software architecture, compositional reasoning algorithms about the behaviors of composite component as well as the protocols of composite interfaces are developed in this paper, which establish a foundation to analyze, validate, simulate composite systems.