The present invention discloses a flip-flop implemented with metal-oxide semiconductors using a single low-voltage power supply and a control method thereof, wherein an external control signal is input to a power switch in order to turn on the power switch for an active mode or to turn off the power switch for a sleep mode and inputting an external sleep control signal; the power switch is used to control a combinational circuit to enter into the active or the sleep mode, and the combinational circuit is connected to a virtual power supply; an internal clock signal is separately input to a master stage and a slave stage of the flip-flop, and whether to enter into the sleep mode or the active mode is determined by the voltage level of the internal clock signal. In the present invention, all the logic gates of the combinational circuit are formed of low-threshold CMOS's, which enables the present invention to maintain a given operation speed at a lower voltage. The flip-flop of the present invention is formed of both low-threshold and high-threshold elements, whereby not only the operation speed can be maintained but also the leakage current can be suppressed spontaneously, and further, the wake-up time can be shortened.