A dual fuel nozzle of a gas turbine combustor with a variable jetting hole diameter is disclosed. The combustor includes a plurality of swirling wings disposed along an outer peripheral surface of a central shaft to have at least one main fuel jetting hole, an air duct positioned at the lower side of the swirling wings to supply air to the swirling wings, a pilot fuel injection hole and jetting hole formed to pass through a central portion of the central shaft to supply a pilot fuel, a switching plate disposed inside the swirling wings to vary the size of the main fuel jetting hole, a driving unit disposed to be connected to the switching plate to move a position of the switching plate, and a casing containing the swirling wings, the air duct, the switching plate and the driving unit. It is possible to enhance fuel flexibility in a multiple fuel system for applying two or more fuels to a gas turbine at the same time.