The oil film lubrication performance of marine stern bearing is impacted by raised temperature and decrease local pressure as it operates with low speeds and heavy loads. The oil film’s level of lubrication has a direct impact on the bearing’s operating condition and lifespan. When operating at low speeds and heavy loads, the lubrication performance (including load capacity and oil film pressure) is greatly affected by the decrease in lubricating oil viscosity brought on by temperature increases and the cavitation of the oil film generated by low local pressure. This study examines the lubrication performance of low-speed plain bearings from the perspectives of cavitation and viscosity-temperature effects. Based on the flow field calculation results, a fluid-structure coupling system of oil-film bearings is built by constructing the viscosity-temperature equation and UDF program. The lubricating oil film and bearing lubrication qualities under different operating situations are systematically computed while taking into account the cavitation effect of the mixed multiphase flow model. The results show that the cavitation region’s maximum oil film pressure, maximum temperature, maximum bearing capacity, and maximum cavitation volume fraction are all lower than those at a particular viscosity. As eccentricity and axial velocity increase, so does the maximum cavitation volume portion.