Bearing is the key component of the traction transmission and wheelset systems of high-speed train. It is possible to experience fatigue damage or failure under the influence of traction motor torque, gear meshing and random wheel-rail excitation during the train operation, which seriously threatens the operation safety of high-speed train. The special complex service conditions of high-speed trains in China require higher fatigue performance and reliability for bearing components, however, the fundamental theory and key technology of fatigue performance and reliability are the weak links in the forward design and development of bearing in China. The research on bearing reliability assessment plays a significant connecting role in solving the bottleneck problem of bearing reliability research. The method and technology of reliability assessment for high-speed train bearings aim to obtain the key mechanical parameters for bearing reliability assessment in service environment, and further to promote the fundamental theory research on bearing fatigue performance and reliability under complex internal and external excitations. Therefore, the key is to identify what mechanical parameters are required for reliability assessment of high-speed train bearings and how to obtain them in such a complex service environment. In this article, the complex service environment and main failure modes of high-speed train bearings during the train operation are firstly reviewed. Then, the key mechanical parameters required for the reliability assessment of high-speed train bearings are proposed and analyzed, in which the important roles of internal rolling-sliding behavior and load distribution on bearing reliability assessment and condition monitoring are emphasized. From the aspects of calculation methods and measurement technologies, the advances to obtain those two key mechanical parameters (i.e. the rolling-sliding behavior and load distribution in bearings) are systematically reviewed. Finally, several open problems in the research of reliability assessment of high-speed train bearing are addressed for future studies.