The invention discloses a garbage and gas-steam combined cycle power generation system adopting gas for drying garbage. The garbage and gas-steam combined cycle power generation system comprises a garbage incineration generator set and a gas-steam combined cycle generator set. The garbage incineration generator set comprises a garbage drier adopting gas for drying garbage, a garbage incinerator, a first turbine and a first generator. The gas-steam combined cycle generator set comprises a gas compressor, a combustion chamber, a turbine, a second turbine and a second generator, all of which are connected in sequence and further comprises a waste heat boiler connected with the turbine through a smoke discharging pipeline, and a second thermodynamic cycle pipeline connected between the waste heat boiler and the second turbine. A smoke pipeline is connected between the waste heat boiler and the garbage drier and is used for leading a small part of low-temperature gas in the waste heat boiler into the garbage drier to serve as a drying heat source for water-containing garbage, and the water-containing garbage can be dried. The garbage and gas-steam combined cycle power generation system has the beneficial effects that the service life of the incinerator is prolonged, the heat efficiency of the incinerator is improved, the combustion supporting coal amount is reduced, and the environment pollution is reduced.