The invention discloses a heating device using a low-grade heat source. The heating device comprises a heat source collector, a gas storage, a vortex tube, a first heat exchanger, a second heat exchanger, a condenser and a solution pump, wherein the gas outlet of the heat source collector is connected with the gas outlet of the gas storage; the top gas outlet of the gas storage is connected with the inlet of the vortex tube; the bottom liquid outlet of the gas storage is connected with the liquid recovery mouth of the heat source collector; the heat end outlet of the vortex tube is connected with a first inlet of the first heat exchanger; the cold end outlet of the vortex tube and the first outlet of the first heat exchanger are respectively connected with a first inlet of the second heatexchanger; a first outlet of the second heat exchanger is connected with the inlet of the condenser; the outlet of the condenser is connected with the inlet of the solution pump; the outlet of the solution pump is connected with the second inlet of the second heat exchanger; and the second outlet of the second heat exchanger is connected with the bottom inlet of the heat source collector. The low-grade heat source can be directly utilized by the device, and the heating device has the advantages of simple structure and energy conservation.