In this paper, a design of current-mode control switching regulator was presented with loop gain analysis. The analysis was verified by the chip implementation and measurement. A current mirror based current sensor was used to sensing the inductor current information. This chip has been fabricated with a TSMC 2P4M 0.35m polyside CMOS process. The measurement result verify the buck converter with on-chip current sensing can operate with load current from 200mA-500mA in a supply voltage from 2.74.2V and the output voltage of 1.8V with no sub-harmonic condition occur. By the loop gain measurement, the correctness of the loop gain analysis is verified. The stability of proposed buck converter was guaranteed by the loop gain measurement, too.