In this paper, an efficient practical method for designing PI controller is proposed. The design is based on optimization of load disturbance rejection with constraint that the Nyquist curve of the loop transfer function is tangent to a line parallel to the imagine axes in the left-half of the complex plane. Thus, it satisfies both robustness and performance requirements. Simulation examples are given to show the effectiveness of the method. The PI formula given in this paper is simple and can be easily adopted by the industry.