Disclosed herein is a method for generating an injected current of fuel cell stack, including: generating a synthesized frequency current in a form in which a first frequency current is synthesized with a second frequency current; and applying the synthesized frequency current to the fuel cell stack, wherein the first frequency current and the second frequency current are each used to calculate at least one of total harmonic distortion and impedance. According to the embodiment of the present invention, a hardware configuration may be reduced by applying the synthesized frequency current of the AC current for calculating the total harmonic distortion (THD) and the AC current for calculating the impedance to the fuel cell stack, without generating the AC current for calculating the total harmonic distortion (THD) and the AC current for calculating the impedance, respectively, thereby reducing a price and a size of the fuel cell stack.