The invention discloses a precharge circuit of a modular multilevel converter and a charge method of the precharge circuit. According to a few of existing methods, submodules of a modular multilevel converter cannot be charged to the condition that capacitor voltage is close to a theoretical operating voltage value, operation is complicated and the charging time is relatively long. The precharge circuit comprises a DC voltage source, a diode, a current-limiting resistor, a first switch, a second switch and a current feed resistor, wherein a positive electrode of the DC voltage source is connected with the positive electrode of the diode through the first switch; a negative electrode of the diode is connected with one end of the current feed resistor and one end of the current-limiting resistor at the same time; the other end of the current feed resistor is connected with the negative electrode of the DC voltage source and a DC bus at the negative electrode of the modular multilevel converter at the same time; the other end of the current-limiting resistor is connected with a DC bus at the positive electrode of the modular multilevel converter; and the second switch is connected with the current-limiting resistor in parallel. According to the precharge circuit and the charge method thereof, the submodules can be directly charged to the condition that capacitor voltage values areclose to a rated operating value in a precharge state, so that the charge method is simple and fast.