A fuel cell system comprising: a first converter , a fuel cell stack and a battery , the first converter being connected to the fuel cell stack and the battery and being configured to convert power, which is output from the fuel cell stack or the battery , into power in a specific level; a second converter configured to convert power which is input to or output from the battery ; a super capacitor ; a power relay assembly configured to control power flow between the super capacitor and the first converter ; and a controller configured to control outputs of the first converter and the second converter , depending on a starting state or an operating state of the fuel cell system, and to control an operation of the power relay assembly , wherein the first converter is disposed on a main bus stage to connect the fuel cell stack to an inverter , and wherein the second converter has one end connected to the main bus stage between the fuel cell stack and the first converter , and an opposite end connected to the battery , and is configured to adjust bi-directional power flow; wherein the power relay assembly has one end connected to the main bus stage between the first converter and the inverter , and an opposite end connected to the super capacitor , and is configured to adjust bi-directional power flow; wherein the second converter is configured to supply starting power of the fuel cell system and charging power of the super capacitor , by using power discharged from the battery , when the fuel cell system is started, and wherein the first converter is configured to supply the charging power, which is received from the second converter , to the super capacitor through the power relay assembly , when the fuel cell system is started. a first converter , a fuel cell stack and a battery , the first converter being connected to the fuel cell stack and the battery and being configured to convert power, which is output from the fuel cell stack or the battery , into power in a specific level; a second converter configured to convert power which is input to or output from the battery ; a super capacitor ; a power relay assembly configured to control power flow between the super capacitor and the first converter ; and a controller configured to control outputs of the first converter and the second converter , depending on a starting state or an operating state of the fuel cell system, and to control an operation of the power relay assembly , wherein the first converter is disposed on a main bus stage to connect the fuel cell stack to an inverter , and wherein the second converter has one end connected to the main bus stage between the fuel cell stack and the first converter , and an opposite end connected to the battery , and is configured to adjust bi-directional power flow; wherein the power relay assembly has one end connected to the main bus stage between the first converter and the inverter , and an opposite end connected to the super capacitor , and is configured to adjust bi-directional power flow; wherein the second converter is configured to supply starting power of the fuel cell system and charging power of the super capacitor , by using power discharged from the battery , when the fuel cell system is started, and wherein the first converter is configured to supply the charging power, which is received from the second converter , to the super capacitor through the power relay assembly , when the fuel cell system is started. <EOS>