The invention relates to a dual fuel combustion-supporting type gas-steam combined cycle system, and belongs to the energy comprehensive utilization technical field. The invention is characterized in that the invention comprises a gas turbine power generating system, a steam turbine power generating system and a circulating fluidized bed boiler; the exhaust tube of the gas turbine of the gas turbine power generating system is communicated with the secondary air inlet tube of the circulating fluidized bed boiler through an exhaust pipeline, the circulating fluidized bed boiler is connected with the steam turbine of the steam turbine power generating system through a steam pipeline, and the steam turbine of the steam turbine power generating system is connected into the economizer of the circulating fluidized bed boiler through a condenser and a feed water pump; a lean fuel supply pipeline is divided into two branch lines, one branch line is led to the combustion engine fuel spraying nozzle of the gas turbine power generating system, and the other branch line is led to the burner of the circulating fluidized bed boiler; an inferior coal-related supply pipeline is accessed to the burner of the circulating fluidized bed boiler. The invention uses the wastes as raw materials to generate electric energy and steam, and thereby primary resource waste and environmental pollution are eliminated, the invention has no secondary pollution, as well as the environment is protected.