A reference voltage circuit is provided, which includes bandgap reference circuit, bias current generator, first capacitor, second capacitor, comparator and control logic circuit. In the active mode of the control logic circuit, the control logic circuit controls the bandgap reference circuit to deliver bandgap reference voltage. The comparator transmits first comparison signal to control logic circuit when the first and second capacitors are charged to the bandgap reference voltage. The control logic circuit enters low power mode and controls the bandgap reference circuit to stop delivering the bandgap reference voltage. If the comparator detects the potential difference between the first capacitor and second capacitor exceeds the threshold value, the control logic circuit returns to active mode according to the second comparison signal transmitted form the comparator.