A capacitor interface circuit is provided. A capacitor under test (CUT) is divided into a variable portion and an invariable portion, and the capacitance of an offset capacitor is designed to equal to or close to the fixed capacitance of the CUT. The offset capacitor is used to store the charges opposite to the invariable portion of the CUT for neutralizing the effect of the invariable portion of the CUT. Thereupon, the charge converter composed by the fully-differential amplifier and the feedback capacitors only responses for the variable portion of the CUT so as to increase the accuracy of the follow-up data processing.