The invention discloses a method and a device for detecting the state of charge of a flow cell system. The method comprises the following steps: acquiring a measured open-circuit voltage obtained by measurement, wherein the measured open-circuit voltage is the real-time detected end voltage of a flow cell system in an open-circuit state; updating voltage parameters used to represent the state of charge according to the measured open-circuit voltage; and determining the real-time state of charge according to the measured open-circuit voltage and the voltage parameters. The technical problem that detection of the state of charge of a flow cell system is inaccurate is solved.