The present invention provides a humidification system for a fuel cell, in which a plurality of membrane humidifiers employing hollow fiber membranes of different kinds having different diameters and pore sizes, or having different numbers of hollow fiber membranes is selectively used according to the amount of current generated from a fuel cell stack or a vehicle output, thus adjusting the humidification amount for dry air to be supplied to a fuel cell stack, and preventing the flooding phenomenon caused at a cathode and the starvation phenomenon in which the air supply is insufficient at the cathode.