As for the design of the flight control system, it is necessary to have good handling qualities as well as having highly stability margin of the system. If feedback gains are merely modified in order to recover the stability margin of the system which is designed regard the closed system response as important, the proper position of poles and zeros collapse, and characteristics of the response receive a bad influence. Lateral-directional flight control system was taken for instance, this paper proposes a technique to design the feedback control law for which to be compatible with both characteristics of the response and the stability very well. Feedback gains are modified to increase the stability margin with that condition of the position of the complex zeros are same as the Dutch roll poles and the position of the spiral pole is coincide with the origin kept by using -90^° phase locus method. This permits a designer to get a control system with large phase margin, and this is especially effective in the case that large delay is entailed in the system.