A fuel cell stack structure (1000; 2000), comprising: first and second cell modules (100, 200), each of which includes one or more fuel cells stacked, the fuel cell including an electrolyte layer, and a cathode layer and an anode layer on both surfaces of the electrolyte layer, respectively, and generating electricity; the fuel cell stack structure (1000; 2000) being characterized in that it further comprises: a first separation plate (300; 350; 700) disposed between a lower surface of the first cell module and an upper surface of the second cell module to be electrically connected to the first cell module; and a second separation plate (400; 450; 800) disposed between the first separation plate (300; 350; 700) and the second cell module to be electrically connected to the second cell module and the first separation plate (300; 350; 700), wherein one of the first separation plate (300; 350; 700) and the second separation plate (400; 450; 800) comprises a protruded convex (330; 380; 720) making contact with the other of the first separation plate (300; 350; 700) and the second separation plate (400; 450; 800) to improve an electrical contact between the first separation plate (300; 350; 700) and the second separation plate (400; 450; 800). first and second cell modules (100, 200), each of which includes one or more fuel cells stacked, the fuel cell including an electrolyte layer, and a cathode layer and an anode layer on both surfaces of the electrolyte layer, respectively, and generating electricity; the fuel cell stack structure (1000; 2000) being characterized in that it further comprises: a first separation plate (300; 350; 700) disposed between a lower surface of the first cell module and an upper surface of the second cell module to be electrically connected to the first cell module; and a second separation plate (400; 450; 800) disposed between the first separation plate (300; 350; 700) and the second cell module to be electrically connected to the second cell module and the first separation plate (300; 350; 700), wherein one of the first separation plate (300; 350; 700) and the second separation plate (400; 450; 800) comprises a protruded convex (330; 380; 720) making contact with the other of the first separation plate (300; 350; 700) and the second separation plate (400; 450; 800) to improve an electrical contact between the first separation plate (300; 350; 700) and the second separation plate (400; 450; 800). a first separation plate (300; 350; 700) disposed between a lower surface of the first cell module and an upper surface of the second cell module to be electrically connected to the first cell module; and a second separation plate (400; 450; 800) disposed between the first separation plate (300; 350; 700) and the second cell module to be electrically connected to the second cell module and the first separation plate (300; 350; 700), wherein one of the first separation plate (300; 350; 700) and the second separation plate (400; 450; 800) comprises a protruded convex (330; 380; 720) making contact with the other of the first separation plate (300; 350; 700) and the second separation plate (400; 450; 800) to improve an electrical contact between the first separation plate (300; 350; 700) and the second separation plate (400; 450; 800).