A capacitance difference detecting circuit with a control circuit, a first capacitor, a second capacitor, a voltage control unit and a computing device. The control circuit generates a control signal according to a first voltage and a second voltage. The voltage control unit cooperates with the first capacitor to be detected and the second capacitor to be detected, according to the control signal, to generate the first voltage and the second voltage. The computing device computes a capacitance difference between the first capacitor to be detected and the second capacitor to be detected according to the first voltage, the second voltage and a parameter of the voltage control unit.