This paper presents a perceptual-control-based agent architecture which enable to construct interactive software system with high usability. Adopting this architecture, the usability requirements can be modeled by adding new architecture levels, in order to realize the orthogonal relationship between different features of usability. And it adopts perceptual-control theory to match the nonlinear relationship between the user-interface and application core. Comparing to the other architectures, systems adopting this architecture can present users with user-interface elements at the user-task level, and permit users to operate the system at the user-task level. The users, therefore, can naturally complete their tasks and reach their goals. Furthermore, the systems adopting the architecture can easily extend the usability dynamically.