Abstract: A method and device of controlling a drain valve of a fuel cell, a controller, a fuel cell system, and a medium is disclosed. The method includes (i) acquiring a permeate water mass flow rate from a cathode to an anode of the fuel cell system and a separation efficiency of a water-gas separator in the fuel cell system, (ii) determining a water mass flow rate level of water passing through a hydrogen circulating pump based on a drive current of the hydrogen circulating pump in the fuel cell system, (iii) determining a circulating water mass flow rate passing through the hydrogen circulating pump based on the permeate water mass flow rate, the separation efficiency, and the water mass flow rate level, and (iv) controlling the drain valve in the fuel cell system based on the circulating water mass flow rate.