In this paper, a high-gain output feedback control structure is applied in order to be optimized with GA for a MIMO nonlinear model of a flight object. In control structure, a modified GA algorithm for obtaining a suitable measurement matrix in feedback loop is proposed which minimizes the interaction between the outputs. The proposed method has two major advantages in compare to other methods; first of all, the proposed method is independent of system degree or system complexity and secondly, in this method some of unknown high-gain method parameters such as arbitrary diagonal matrix, etc are discarded. Computer simulations are carried out for showing the performance of the designed controller against common high-gain controller.