The present invention provides a method for controlling the amount of air supplied to a fuel cell, which can prevent flooding and membrane dry-out in a fuel cell stack and, at the same time, ensure optimal performance of the fuel cell stack and a humidifier by supplying an optimal amount of air to the fuel cell stack at each operation condition.For this purpose, the present invention provides a method for controlling the amount of air supplied to a fuel cell, the method including measuring the temperature and pressure of humidifier outlet (stack inlet) air, the temperature and pressure of stack outlet air, and the relative humidity of the humidifier outlet (stack inlet) air, and determining the stoichiometric ratio of air or the amount of air supplied to the stack based on the measurement results so as to adjust the relative humidity of the stack outlet air reach a target value.