Generally, industrial processes are too complex to obtain precise dynamics of a plant. Therefore, a controller is required to have robustness property in that it can attain acceptable control performance and closed-loop stability in the presence of plant uncertainty. In this paper, we proposed the unified design method for robust PID controller with two degrees of freedom which satisfies multiple design specifications based on the matrix inequality approach. And we propose a new genetic algorithm for solving this matrix inequality problem, because this problem is not formulated as the linear matrix inequality problem. And this method demonstrated by numerical simulations and shows good performance.