The utility model relates to a thermal difference engine unit which comprises a high temperature heat source heat exchanger, a low temperature heat source heat exchanger, an engine mainframe, a speed controller and an actuating medium conveyance controller, wherein the high temperature heat source is led into the high temperature heat source heat exchanger to exchange heat with the actuating medium in a high pressure chamber, so that the actuating medium is vaporized or the actuating medium with high temperature generates high voltage. Vaporized high pressure actuating medium or high pressure actuating medium with high temperature enters a cylinder of a temperature difference engine through the speed controller to push a piston or a rotor to work and output power. The expanded actuating medium enters a low pressure cavity of the low temperature heat source heat exchanger to exchange the heat with the low temperature heat source. The actuating medium is liquified or the temperature of the actuating medium is reduced, and then, the actuating medium is conveyed back to the high pressure chamber through the actuating medium conveyance controller. The utility model makes use of the carbon dioxide compressed gas as the energy storage, can convert the various residual heat into power, and make the residual heat fully used. The utility model has no environmental pollution and is a power unit with environmental protection.