The invention discloses a gas-steam combined circulation system and an operation control method thereof. The gas-steam combined circulation system comprises a gas turbine, a steam circulation loop, a hot water generator, an absorption refrigerator and a gas-water heat exchanger, wherein a waste heat boiler, a steam turbine and a steam condenser are arranged on the steam circulation loop; the hot water generator is communicated with a smoke outlet of the waste heat boiler; the absorption refrigerator is communicated with the hot water generator by a refrigeration driving circulation pipeline; a water side of the gas-water heat exchanger is communicated with the hot water generator by a heating circulation pipeline and is communicated with the absorption refrigerator by a refrigeration circulation pipeline, and a gas side of the gas-water heat exchanger is communicated with a gas inlet of the gas turbine. According to the gas-steam combined circulation system and the operation control method thereof disclosed by the invention, the temperature of air entering the gas turbine is adjusted by pre-heating or pre-cooling, so that the efficiency of the whole gas-steam combined circulation system is optimal. Meanwhile, the gas-steam combined circulation system recycles low-grade waste heat of a power plant, and steam does not need to be extracted out of a steam extraction opening of the steam turbine as a heat source, thereby avoiding the occurrence of a phenomenon of energy waste and ensuring the output and the efficiency of the steam turbine.