A converter valve basic control device for a flexible direct current transmission system based on a module multilevel converter, the module multilevel converter being provided with a bridge arm comprising a plurality of cascaded sub-modules, the converter valve basic control device comprising the following components structured in a hierarchical control architecture: a current control unit used for controlling a current of the converter, for generating in real time the number of the sub-modules of the bridge arm to be input, for obtaining a current direction of the bridge arm and for outputting the number information and the current direction information; wherein the current control unit receives real-time values of capacitor voltages of the sub-modules of the bridge arms and the current of the bridge arms, and generates additional adjustment values of real-time reference voltages of the bridge arms, which are used for carrying out a modulation operation, the purpose of which is to convert the real-time reference voltages into the number of the converter sub-modules needing to be input by the bridge arms in real time; a bridge arm summary control unit used for determining sub-modules to be input or removed according to the received state of each sub-module and according to the number information and the current direction information received from the current control unit, and which outputs the determined result; and a bridge arm segmented control unit used for inputting or removing the sub-modules according to the determined result received from the bridge arm summary control unit, and which obtains the state of each sub-module and sends the state to the bridge arm summary control unit, characterised in that the current control unit, the bridge arm summary control unit and the bridge arm segmented control unit are all of a dual redundancy design in which the current control unit, the bridge arm summary control unit and the bridge arm segmented control unit are respectively divided into a system A and a system B, wherein the systems A and B are respectively connected with the systems A and B of an upper level control unit, and a switch-over mechanism between master and standby systems guarantees that the system B can be quickly operated in the case of a fault of the system A, while the system A can quickly react and be quickly operated in the case of a fault of the system B. a current control unit used for controlling a current of the converter, for generating in real time the number of the sub-modules of the bridge arm to be input, for obtaining a current direction of the bridge arm and for outputting the number information and the current direction information; wherein the current control unit receives real-time values of capacitor voltages of the sub-modules of the bridge arms and the current of the bridge arms, and generates additional adjustment values of real-time reference voltages of the bridge arms, which are used for carrying out a modulation operation, the purpose of which is to convert the real-time reference voltages into the number of the converter sub-modules needing to be input by the bridge arms in real time; a bridge arm summary control unit used for determining sub-modules to be input or removed according to the received state of each sub-module and according to the number information and the current direction information received from the current control unit, and which outputs the determined result; and a bridge arm segmented control unit used for inputting or removing the sub-modules according to the determined result received from the bridge arm summary control unit, and which obtains the state of each sub-module and sends the state to the bridge arm summary control unit, characterised in that the current control unit, the bridge arm summary control unit and the bridge arm segmented control unit are all of a dual redundancy design in which the current control unit, the bridge arm summary control unit and the bridge arm segmented control unit are respectively divided into a system A and a system B, wherein the systems A and B are respectively connected with the systems A and B of an upper level control unit, and a switch-over mechanism between master and standby systems guarantees that the system B can be quickly operated in the case of a fault of the system A, while the system A can quickly react and be quickly operated in the case of a fault of the system B.