A capacitance difference detecting circuit includes a control circuit, for generating a control signal according to a first voltage and a second voltage; a first capacitor to be detected; a second capacitor to be detected; a first constant capacitor, having a terminal coupled to the first terminal of the first capacitor to be detected and the first input terminal; a second constant capacitor, having a terminal coupled to the first terminal of the second capacitor to be detected and the second input terminal; a voltage control unit, cooperating with the first capacitor to be detected, the second capacitor to be detected, the first constant capacitor and the second constant capacitor to control the first voltage and the second voltage. The voltage control unit is an adjustable capacitor and a capacitance value of the adjustable capacitor is controlled by the control signal.