This paper analyzes the effects of air in the oil film of a tilting-pad journal bearing on oil–air distributions and characteristics. With a gaseous cavitation model and shear stress transport model with low-Re correction included, the air backflow from the outlet boundary is analyzed in numerical simulations of a titling-pad journal bearing at 3000 r/min rotation speed and under 180 kN load. The simulated bearing load, pressure, and mechanical loss are in good accordance with the experimental data, indicating that the simulation results of the air backflow from the outlet boundary can catch the hydrodynamic characteristics accurately. Based on the turbulence viscosity ratio analysis, the turbulence effect cannot be ignored at the high rotational speed. With the comparison between the unloaded area and the loaded area, the boundary layer and turbulent flow develops with the film thickness increasing. Based on the analyses of simulated air volume fraction and pressure distribution, the gaseous cavitation occurs around the center part of the unloaded area, following the gaseous cavitation mechanisms. The backflow air flows into the low-pressure unloaded area from the outlet boundary and has a clear interval with the air from the gaseous cavitation. The air volume fraction increases with these two air sources and affects the mixture viscosity significantly, eventually influencing the shear stress on the rotor-side wall and bearing mechanical loss.