The present invention relates a method of supplying fuel to a fuel cell, which comprises steps of: feeding a specific amount of a fuel into a fuel cell; obtaining a second characteristic value at a specific time point; detecting and measuring a character of the fuel cell at a time interval before the specific time point for obtaining a second characteristic value; comparing the second characteristic value to the first characteristic value for enabling the fuel to be fed into the fuel cell while the second characteristic value is smaller that the first characteristic value. By the aforesaid method, the supplying of fuel to the fuel cell can be effectively controlled for optimizing the performance of the fuel cell without the use of fuel sensor required thereby and thus reducing the cost and complexity of manufacturing the fuel cell system.