Multi-stage in-line cartridge ejectors for a fuel cell system provided herein comprise: at least one ejector main body for supplying hydrogen, each ejector main body including a plurality of nozzles arranged in line with a predetermined gap, in which the diameters of the respective nozzles become larger from an inlet side of the ejector main body toward an outlet side thereof, and a plurality of sub-inlets formed on an outer surface of the ejector main body to be connected to the gap or gaps between the nozzles; and a housing accommodating the eject main body and including a main inlet for intake of recirculated hydrogen. The multi-stage in-line cartridge ejectors can improve the system performance by increasing the amount of recirculated hydrogen. Moreover, at least one check valve is provided at an intake position of the cartridge ejectors to effectively prevent reverse flow of recirculation hydrogen gas and at least one heater is provided around the cartridge ejectors to improve cold startability.