Non-contact face seal has a stable operation and no direct friction between the faces， which can greatly extend the seal life and has a wide application prospect as a shaft seal for various rotary machinery. Non-contact face seals are designed with a configuration on the face to produce a hydrodynamic pressure effect to improve the load carrying capacity of the seal. This paper describes the influence of groove shapes， face deformation， temperature-stick effect and cavitation effect on the hydrodynamic pressure effect of face seals， summarizes the current research status on the theory， experiment and application of hydodynamic pressure effect， and prospects the future development direction of non-contact face seals.