Modular multilevel converter (MMC) has been widely applied in the VSC-HVDC (voltage source converter-high voltage direct current transmission) field.In MMC application,it is very difficult to upgrade the program of the sub-modules of MMC.The structure of VSC-HVDC control system and sub-module of MMC is described,the program function of sub-module controller is analyzed.A method of program remote upgrade for MMC is introduced,the design of main hardware modules and software flowchart of the program upgrading system is presented.Safety and reliability evaluation of program remote upgrade for MMC is also described.This work is applied and verified based on dynamic simulation experiment platform for MMC research.