An adaptive time constant matching Gm-C inductor current sensing method is proposed. By comparing the zero-crossing time difference between the SW voltage of buck converter and the Gm-C filtering sensing voltage, the control loop determined whether the Gm-C time constant matched the DCR time constant. A phase/frequency detector was adopted to detect the time difference. The phase/frequency detector also controlled the reversible counter to calibrate the equivalent capacitance of the capacitor array. Finally, the adaptive time constant matching Gm-C inductor current sensing was implemented. Compared with previous works, the calibration process is smooth, and the DC-DC converter can be modulated online under the normal working condition, which can effectively adapt to the change of external conditions, such as temperature, voltage and current, in the operation of the DC-DC converter.