The invention discloses a gas depressurizing heating device and a gas depressurizing heating method. The gas depressurizing heating device comprises a vortex tube, a high pressure pipeline and a low pressure pipeline, wherein the vortex tube is connected with a cold flow output pipe and a hot flow output pipe; and the vortex tube is provided with a pressure relief nozzle. The device further comprises a cooling device and a heat conduction piece, wherein the cooling device and the heat transmission piece are arranged on the cold flow output pipe; and one end of the cold flow output pipe is connected with the vortex tube, and the other end of the cold flow output pipe is communicated with the hot flow output pipe and further communicated with the low pressure pipeline. The gas depressurizing heating method comprises the following steps: partial heat of the vortex hot flow is conducted through the pressure relief nozzle, and the vortex cold flow is heated by the cooling device and joins the vortex hot flow so as to output low pressure gas. The pressure relief nozzle is heated through the heat conduction piece, thereby preventing frost block; the vortex cold flow is heated by the cooling device and is further mixed with the vortex hot gas, so that the temperature of the low pressure gas discharged is increased without extra energy; and meanwhile other products can be produced using the cooling device, so that energy-saving circular economy is realized.