For the lower cost and shorter drilling cycle, oil-based mud is widely used in drilling highly deviated directional wells, horizontal wells, and various complex formations. However, oil-based mud invades the formation and changes the physical properties of the formation around the well, which bring great challenges to fluid identification and reservoir evaluation. In order to figure out the influence of oil-based mud invasion on NMR logging response, this paper selected the cores of tight sandstone and conglomerate reservoirs in ultra-deep wells in the southern margin of Junggar Basin, Xinjiang, and carried out three groups of petrophysical experiments, including composition of oil-based mud, oil-based mud displacement, and oil-based mud imbibition, and the variation characteristics of nuclear magnetic resonance T2 spectrum during the experiment were analyzed simultaneously. The results show that the base fluid components in the oil-based mud can not only invade the formation around the well under positive differential pressure but also infiltrate into the formation through buoyancy and capillary force. When the formation contains water/oil, the invasion of base fluid will cause the transverse relaxation time and spectral peak of micropore T2 spectrum (<10ms) to decrease, and the spectral peak will gradually shift to the left; The T2 spectrum peak (>100ms) of mesopores moves to the right and the area increases; The above T2 spectrum change rate is mainly affected by formation permeability, invasion time and temperature, but limited by mud type, oil-water ratio, and other factors.