The material characteristics and one of the preparation methods, atomic layer deposition of Al2O3 are introduced. The passivation mechanisms (chemical passivation and field-effect passivation) of Al2O3 films are demonstrated comprehensively, and optimization methods from the angles of film thickness, thermal stability and stack passivation are illuminated. The application of Al2O3 passivation in the crystalline silicon solar cell is provided, including passivated emitter rear locally diffused cell and passivated emitter and rear cell. Finally, the future study of the Al2O3 passivation process and the application to industry production are proposed.