A capacitive fingerprint sensor is provided. The capacitive fingerprint sensor includes a sensing array, an insulating surface disposed on the sensing array, and a readout module. The sensing array includes a plurality of sensing units, and each of the sensing units includes a sensing capacitor and a reference capacitor. When a finger contacts the insulating surface, the readout module obtains a sensing time interval corresponding to the sensing capacitor of each of the sensing units and a reference time interval corresponding to the reference capacitor of each of the sensing units during a sensing period. The readout module provides a sensing output according to the sensing time interval and the reference time interval to indicate a fingerprint ridge or a fingerprint valley of the finger.