The invention relates to a state prediction method for submodules of a modular multilevel converter. The method comprises the following steps: carrying out failure state prediction on switching timesof all the submodules within a period of time, wherein the failure possibility of the submodules is improved along with the increase of the switching times of the submodules; recording the switching times of all the submodules, then sorting all the submodules from high to low according to the switching times of the submodules, or calculating the average switching time of all the submodules; sorting all the submodules from high to low according to a difference between the switching times and the average switching time of all the submodules, or recording the switching times of all the submodulesand then sorting all the submodules according to a difference between the switching times of all the submodules and a preset switching time standard value, so as to obtain failure possibility sortingof all the submodules. According to the state prediction method disclosed by the invention, the submodules with abnormal parameters and the submodules with higher failure possibility can be effectively picked out and further provide auxiliary information for operation and maintenance of a flexible direct current system, so that the pertinence of maintenance work of the flexible direct current system is improved.