In present paper ,I Investigated the problems of designing the PI controllers for robust performance and stability for an arbitrary-order SISO(single Input and single output) linear time-invariant plant or system concerned with the problems of both structured and unstructured uncertainities.For achieving the robust stability for plant under the effect of uncertainities, I will convert all the problems into the segments of Qusipolynomial equations. The results on H∞ PI designing or tuning are then used into a programming design techniques for obtainig the values of required PI (proportional and integral) gains (Kp,Ki). Main important charactersitic of the given method is that it constructively characterizes the entire set of tuned PI controllers. This characterization can provide the optimal tuning of PI controller for the required design. KeywordsPI Controller , Structure uncertainity,Robust Stability, Frequency domain,Sensitivity, Unstructured uncertainity .