A new design method of multivariable static output feedback H_∞fixed-order PI controller for aero-engine is presented.The synthesis of H_∞fixed-order controller can be formulated as a Bilinear Matrix Inequality (BMI) optimization problem which is hard to solve.But under certain aero-engine conditions

the BMIs raised in the H∞fixed-order design problem can be converted into standard Linear Matrix Inequalities (LMIs).Then the existence condition of H_∞fixed-order controller is deduced and the design procedures of the controller are proposed.The approach proposed in the paper has been successfully applied to turbo-engine fixed-order PI controller design.The simulation results show that the performance and robustness of controlled system are satisfied.