Abstract: Liquid face seals are the main form of shaft end seal used in process industry, which are widely applied to aerospace, marine engineering equipment and high-end manufacturing equipment. A phase change may take place as the liquid flows through the seal clearance, which leads to the seal either face deformation, dry friction or even failure. It is of great significance to carry out the research on the liquid face seal of vapor-liquid two-phase flow because phase changes may affect the safe, reliable and stable operation of relevant equipment or even the whole device. This paper summarized the research status of the liquid face seal of vapor-liquid two-phase flow in the past 50 years. Typical heat sources and heat transfer in the seal plates were concluded. The principle of the phase change of liquid face seals was expounded in this paper. The measurement techniques of end-face fluid film parameters were summarized. On experimental research, the influences of the operation condition, geometrical dimensions, surface morphology or surface texture on a phase change to vapor were significant. Attention to inlet and outlet conditions, balance ratio and face deformation was attached, however, not enough to surface morphology, surface texture and friction pairs. On theoretical research, criteria for stability of face seals and three models (Discontinuous Boiling Model, Continuous Boiling Model, Film Homogenous Boiling Model) of analyzing the phase change and of advantages, disadvantages and suitable ranges were presented. It was proposed that establishing a more accurate theoretical model of vaporization of the fluid between the faces of a mechanical seal, realizing the stable operation and breaking through the key monitoring technology of mechanical face seals with a phase change, and building an intelligent liquid face seals were the emphases for research in the future.