The invention discloses a nuclear magnetic resonance instrument probe auxiliary device for carrying out steam saturation on porous media. The device comprises a probe tube internally filled with porous media samples, wherein a vacuum pump is connected above the probe tube; a water tank, a saturation device and a heating device are connected under the probe tube; the water tank and the saturation device are heated by the heating device and then convey steam into the probe tube; and the vacuum pump can be used for vacuuming the samples in the probe tube, so that air, liquid and impurities in pores of the samples are cleaned. Compared with a traditional nuclear magnetic resonance core detection device, through saturation of the steam, the problem of insufficiency in saturation of fine pores of the samples is solved. Due to the design of the saturation device, the heating device and the vacuum device connected with a probe, the temperature and a sealing state of the samples in an experiment process are ensured, and the detection precision and the accuracy of nuclear magnetic resonance on the core samples are promoted.