Modular multilevel converter (MMC) system with high voltage and capacity has been widely applied among the VSC-HVDC projects in the world.In MMC application,capacitor voltage balancing ranking algorithms became a hot topic.This paper respectively focused on voltage balancing ranking algorithms suited for high-level MMC to summarize the state of the art literatures of this field methodically,and then to explore the cutting-edge research to show the core issues and concerns in the area.The sorting methods are clarified according to the purposes of reducing time complexity or switching frequency and the collective main ideas of them are extracted.This paper also explored the evaluating indicators for MMC ranking algorithms.By simulations,the capacitor voltage balancing effects of three algorithms with different complexities are compared.The switching frequencies of algorithms with maintaining factor are measured.In the end of this paper,the development direction of ranking algorithms in FPGA (field program gate array) for MMC real-time simulation is discussed.