The present invention provides a steam injection heatpump heating system. The technical solution is that the system is composed of a steam injector, a high voltage steam pipeline, a low voltage steam pipeline, a throttling gear and a bypass connecting pipe. The high voltage steam enters in the heat exchanger heaing backwater after injecting lower steam turbine voltage condensing in low temperature, this realises waste heat recovery in low temperature condensing steam of the steam turbine. The core component is the steam injector, the high voltage heat supplying pumping is used as high-velocity jet acceleratively formed in the injecting tube of the working steam, and lower voltage steam turbine is rolled in the mixing room as injected flow, mixing steam in the expanding section of the steam injector is decelerately compressed in a certain back pressure, then sending to the heat interchanger for heating backwater, a certian back pressure mixing steam condenses to water after heat releasing in the exchanger, returning to the backwater system of electrical factory, completing thermal circuit of the combined heat and power generation set.