A method for controlling output of inverters and a fuel cell in a fuel cell system, comprising: a first step allocating a serial number to each inverter; a second step determining for an inverter selected out of said inverters whether the serial number is 1; a third step determining whether a grid frequency f is within a range of a second minimum frequency value and a second maximum frequency value which are predetermined within a reference range spanning from a first minimum frequency value to a first maximum frequency value; a fourth step normally operating said selected inverter; a fifth step determining whether the voltage output of said selected inverter is within a normal range; a sixth step determining whether the current output of said selected inverter is within a normal range; a seventh step normally operating said selected inverter; an eighth step determining whether the grid frequency f is within a range of the first minimum frequency value and the first maximum frequency value; a ninth step determining whether the serial number of said inverter selected out of said inverters is 2 if it is determined in the second step that the serial number is not 1; a tenth step determining whether the grid frequency f is within a range of a third minimum frequency value and a third maximum frequency value; an eleventh step normally operating said selected inverter; a twelfth step keeping said selected inverter at stand by if it is determined in the third step that the grid frequency f is not between the second minimum frequency value and the second maximum frequency value; a thirteenth step determining whether said selected inverter state is checked; a fourteenth step determining, periodically, whether the grid frequency is normal; a fifteenth step determining whether the grid frequency f is between the first minimum frequency value and the first maximum frequency value; a sixteenth step displaying a voltage error if it is determined in the fifth step that the voltage is not within the normal range; a seventeenth step displaying a current error if it is determined in the sixth step that a current is not within the normal range; an eighteenth step displaying a grid frequency error if it is determined in the eighth step that the grid frequency is not between the first minimum frequency value and the first maximum frequency value; and a nineteenth step stopping said selected inverter if it is determined in the thirteenth step that the inverter state is not checked, or if it is determined in the fifteenth step that the grid frequency is not between the first minimum frequency value and the first maximum frequency value, or if the sixteenth, seventeenth, and eighteenth steps are performed. a first step allocating a serial number to each inverter; a second step determining for an inverter selected out of said inverters whether the serial number is 1; a third step determining whether a grid frequency f is within a range of a second minimum frequency value and a second maximum frequency value which are predetermined within a reference range spanning from a first minimum frequency value to a first maximum frequency value; a fourth step normally operating said selected inverter; a fifth step determining whether the voltage output of said selected inverter is within a normal range; a sixth step determining whether the current output of said selected inverter is within a normal range; a seventh step normally operating said selected inverter; an eighth step determining whether the grid frequency f is within a range of the first minimum frequency value and the first maximum frequency value; a ninth step determining whether the serial number of said inverter selected out of said inverters is 2 if it is determined in the second step that the serial number is not 1; a tenth step determining whether the grid frequency f is within a range of a third minimum frequency value and a third maximum frequency value; an eleventh step normally operating said selected inverter; a twelfth step keeping said selected inverter at stand by if it is determined in the third step that the grid frequency f is not between the second minimum frequency value and the second maximum frequency value; a thirteenth step determining whether said selected inverter state is checked; a fourteenth step determining, periodically, whether the grid frequency is normal; a fifteenth step determining whether the grid frequency f is between the first minimum frequency value and the first maximum frequency value; a sixteenth step displaying a voltage error if it is determined in the fifth step that the voltage is not within the normal range; a seventeenth step displaying a current error if it is determined in the sixth step that a current is not within the normal range; an eighteenth step displaying a grid frequency error if it is determined in the eighth step that the grid frequency is not between the first minimum frequency value and the first maximum frequency value; and a nineteenth step stopping said selected inverter if it is determined in the thirteenth step that the inverter state is not checked, or if it is determined in the fifteenth step that the grid frequency is not between the first minimum frequency value and the first maximum frequency value, or if the sixteenth, seventeenth, and eighteenth steps are performed.