The invention relates to a buck-type angle-type STATCOM and a control method thereof, According to the connection group of step-down transformer and the principle of ideal transformer, the voltage ofthree-phase high-voltage side of step-down transformer is converted to three-phase line voltage of ideal low-voltage side, and the three-phase voltage of high-voltage side is phase-separated controlled by phase-separated control of line voltage between three phases of ideal low-voltage side. The invention effectively solves the problems of inaccurate phase separation control and coupling control between three phases due to the non-corresponding relationship between the reactive current of the converter chain and the three-phase voltage of the high-voltage side when the reactive current of theconverter chain is directly used for phase separation control.