Abstract: The order of helicopter controller is usually high.How to reduce the order of controller as much as possible and preserve the performance of closed-loop system is a problem which needs solving.In this paper,a Krylov subspace method is applied to H_∞ controller reduction of UH-60A helicopter.It is shown that the proposed method can not only match the desired closed-loop system responses,but also does not need solving any Lyapunov equations and using computational tools,greatly reducing computation work.The simulation results also show the effectiveness of the method.