The invention discloses a mid-infrared laser efficiency improving method and a mid-infrared laser device. The mid-infrared laser device comprises a pumping source, a laser crystal and a resonant cavity; the laser crystal is arranged in the resonant cavity; the pumping source emits pumping light; the pumping light enters the laser crystal; the energy levels of the laser crystal at least comprise a ground state, a first excited state and a second excited state in a high-to-low order; and after the laser crystal is excited, population inversion occurs on the laser crystal, and the laser crystal generates first wavelength laser and second wavelength laser, wherein the first wavelength laser is mid-infrared laser which is generated by particle transition from the second excited state to the first excited state, and the second wavelength laser is laser which is generated by particle transition from the first excited state to the ground state. According to the mid-infrared laser efficiency improving method and the mid-infrared laser device of the invention, the resonant cavity structure is designed, so that the mid-infrared laser and the laser corresponding transition from mid-infrared laser lower-energy levels to the ground state can be outputted simultaneously, so that mid-infrared laser lower-energy level particles can fall to the ground state quickly, and therefore, the service lives of lower-energy level particles of the laser crystal can be shortened, and the efficiency of the laser can be improved, and dual-wavelength laser output can be realized.