In order to improve the efficiency of geothermal energy extraction in the hightemperature zone at the bottom of the well, a jettype coaxial borehole heat exchanger is constructed for horizontal geothermal well extraction. Based on the finite volume method, a threedimensional numerical simulation model of the horizontal section near the bottom of the well is established, and the flow and temperature fields of the Outsidein and insideout type (OI), Insideout type (IO), and Jet inlet (IOI) coaxial borehole heat exchangers are compared and analyzed, so as to reveal the mechanism of the injection heat exchanger to strengthen the heat transfer. The results showed that the use of the IOI type heat exchanger increased the turbulent kinetic energy of the fluid and formed vortices, which improved the efficiency of geothermal heat extraction. By comparing the heat extraction performance, it was found that the Nusselt number increased with the increase of mass flow rate, and the Nusselt number of IOI type was higher than the other two by 18.33%~32.48% and 5.33%~18.84%, and the friction coefficient decreased with the increase of mass flow rate; under the same mass flow rate, the thermal enhancement factor of IOI type heat exchanger was higher than the other two by 9.13%~13.58%, 3.61%~10.24%, and the average extraction temperature and average extended metre heat exchange are always the highest among the three. The results provide a theoretical basis for the efficient extraction of coaxial borehole heat exchanger in horizontal geothermal wells.