A steam iron adapted for ironing a piece of cloth with steam generated thereby, said steam iron including: a machine body unit; a sole plate unit connected to a bottom end of said machine body unit; a water supply unit connected to said machine body unit; and a heating unit connected to said sole plate unit and heating up said sole plate unit so that the water supplied to said sole plate unit is heated to form the steam, a control unit connected to said machine body unit, measuring moving speed of said steam iron and; the steam iron being characterized in that: the water supply unit includes a pump that is adapted for supplying water to said sole plate unit, the control unit controlling water output of said pump based on the moving speed of said steam iron wherein said control unit includes a three-axis accelerometer and a control circuit that is electrically connected to said three-axis accelerometer and said pump of said water supply unit; wherein said three-axis accelerometer measures acceleration of said steam iron and transmits a measured signal to said control circuit; wherein said control circuit transmits a control signal to said pump based on the measured signal such that said pump supplies a corresponding amount of the water to said sole plate unit based on the control signal; and wherein said control unit further includes an air spray switch that is electrically connected to said control circuit and that is operable to control said control circuit to increase the amount of the water supplied to said sole plate unit by said pump such that steam output of said steam iron is increased. a machine body unit; a sole plate unit connected to a bottom end of said machine body unit; a water supply unit connected to said machine body unit; and a heating unit connected to said sole plate unit and heating up said sole plate unit so that the water supplied to said sole plate unit is heated to form the steam, a control unit connected to said machine body unit, measuring moving speed of said steam iron and; the steam iron being characterized in that: the water supply unit includes a pump that is adapted for supplying water to said sole plate unit, the control unit controlling water output of said pump based on the moving speed of said steam iron wherein said control unit includes a three-axis accelerometer and a control circuit that is electrically connected to said three-axis accelerometer and said pump of said water supply unit; wherein said three-axis accelerometer measures acceleration of said steam iron and transmits a measured signal to said control circuit; wherein said control circuit transmits a control signal to said pump based on the measured signal such that said pump supplies a corresponding amount of the water to said sole plate unit based on the control signal; and wherein said control unit further includes an air spray switch that is electrically connected to said control circuit and that is operable to control said control circuit to increase the amount of the water supplied to said sole plate unit by said pump such that steam output of said steam iron is increased. the water supply unit includes a pump that is adapted for supplying water to said sole plate unit, the control unit controlling water output of said pump based on the moving speed of said steam iron wherein said control unit includes a three-axis accelerometer and a control circuit that is electrically connected to said three-axis accelerometer and said pump of said water supply unit; wherein said three-axis accelerometer measures acceleration of said steam iron and transmits a measured signal to said control circuit; wherein said control circuit transmits a control signal to said pump based on the measured signal such that said pump supplies a corresponding amount of the water to said sole plate unit based on the control signal; and wherein said control unit further includes an air spray switch that is electrically connected to said control circuit and that is operable to control said control circuit to increase the amount of the water supplied to said sole plate unit by said pump such that steam output of said steam iron is increased.