A capacitive sensor with a calibration mechanism is provided. The capacitive sensor includes a set of sensing capacitors to generate a capacitance variation, a subtraction circuit and an integration circuit. The subtraction circuit includes a first capacitor array to generate offset-adjusting charges and a second capacitor array to generate subtraction charges according to an initial offset and a sensitivity of the sensing capacitors respectively. The integration circuit includes two input ends, wherein one of them is connected to the sensing capacitors and the subtraction circuit. During a sensing period, the integration circuit performs integration according to the capacitance variation and performs cancellation of the effect of the initial offset according to the offset-adjusting charges to generate an integration output signal that is continuously subtracted by the subtraction charges during a computing period to generate a subtraction count. A capacitive sensing method is disclosed herein as well.