The invention relates to the technique for cooling hot gas, particularly to a temperature reduction method for hot gas and a device thereof. At present, the method for reducing temperature by spraying is used widely, which not only increase the composition of hot gas and the volume flow, but also increase the investment of system, with low heat exchange efficiency and difficulty to control the process. The invention comprises a tube bundle heat exchanger canister, an outer jacket of a tube bundle cooler, a light tube heat exchange unit, and a finned tube heat exchange unit. The light tube heat exchange unit and the finned tube heat exchange unit are orderly disposed inside of the tube bundle heat exchanger canister. The outer jacket of a tube bundle cooler is fixedly disposed on the outerwall of the tube bundle heat exchanger canister. The hot gas is cooled by air exchanging heat with recycled cooling water by entering the tube bundle heat exchanger. By adopting the tube bundle heat exchanger, with the outer jacket opening, the invention can efficiently decrease the temperature of the tube bundle heat exchanger, decrease the load of canister, reduce the thickness of the canister,and lower the investment.