The invention discloses a dual-gas-fuel combustor and a gas turbine operation method using the same. Combustion of auxiliary fuel, namely natural gas, is utilized to serve as a combustion-stabilizingfire source so that synthesis gas can be combusted stably within a wide flow range (30-115% of rated flow), and vibration caused by unstable combustion can be reduced. When a power grid requires an IGCC to quickly increase/reduce the load but the yield of the synthesis gas cannot be quickly changed due to slow load change of a gasification furnace, the load of a gas turbine can be quickly changedto meet the requirement of the power grid by quickly increasing/reducing the flow of the auxiliary natural gas and switching part of natural gas/synthesis gas channels to greatly and quickly increasethe flow of the natural gas.