The invention discloses a current-limiting UPFC (Unified Power Flow Controller) direct-current side overvoltage protection system. The current-limiting UPFC direct-current side overvoltage protection system comprises an overvoltage protection circuit, a parallel converter and a serial converter which are connected in parallel to the two ends of a direct-current capacitor of the current-limiting UPFC, wherein the parallel converter is connected with a parallel transformer through a first filtering inductor; the serial converter is connected with a serial transformer through a second filtering inductor; the other end of the serial transformer is connected with a current limiter; the overvoltage protection circuit comprises a current-limiting resistor, a diode, a breakdown diode, a filtering resistor, a filtering capacitor, an IGBT, an IGBT driving circuit and a discharging resistor; the overvoltage protection circuit is triggered through the breakdown diode; the IGBT is taken as a switch of a discharging branch; the breakdown diode is in series connection with the current-limiting resistor; the diode is used for preventing the breakdown diode from carrying reverse voltage; the filtering resistor and the filtering capacitor construct a low-pass filtering branch for preventing the IGBT from being wrongly triggered; a negative electrode of the breakdown diode and a controller signal are connected to the IGBT driving circuit through an OR gate.