Aimed at the occurrence of high temperature alarm of the stern tube bearing on board during the ship building tests in berth and voyage, the mathematical model for the lubrication mechanism between the surface of tail shaft and bearing was established. The effects of the rotation rate of tail shaft and kinematic viscosity of lubricants on the oil film pressure distribution between tail shaft and stern tube bearing and bearing capacity were studied, the main reasons that caused the occurrence of high temperature alarm of stern tube bearing were analyzed. The results show that the kinematic viscosity of the used environmentally acceptable lubricant is too low, and the tail shaft runs for a long period of time at low speed region during the ship building tests in berth and voyage, which are the main reasons to cause the occurrence of high temperature alarm of stern tube bearing. The high temperature phenomena of stern tube bearing can be reduced or avoided by improving viscosity of lubricant and avoiding the tail shaft to run for a long period of time at low speed region.