In this paper, we propose the Improved SIR-based Power Control method in mobile communication system. Generally speaking, SIR-based design considering both channel noise and multiuser interference is accurate indication of signal quality and provides good performance. However, one serious problem associated with SIR-based Power Control is the potential of Positive Feedback which can endanger the stability of the system. Therefore from SIR definition, we decrease the signal`s Interference we will got a improved SIR and have a stable power control Also in mobile using window register which has Up-Maintain-Down power control step size instead of Up-Down, we got a better performance. This paper assesses the performance of Improved SIR based Power Control using PIC and window register. The proposed Improved SIR based Power Control is presented and compared with existing SIR based Power Control and Strength-and-SIR based Power Control.