In this paper, an improved decentralized control method is proposed to design a bank-to-turn (BTT) missile autopilot. Compared to the general diagonal blocked Lyapunov function method, the improved decentralized control method by considering the coupling terms as the structured uncertainty can provide a simpler design, tolerate more types of uncertainties and yield a better dynamic performance. Moreover, this method can be extended to multimodel systems expediently. Due to the structural constraints, the decentralized controller may not realize the tracking control target under some conditions, and this paper also provides such a condition. The decentralized controller design is formulated in terms of linear matrix inequality (LMI) optimization, and the simulation results demonstrate the effectiveness of the proposed method.