The -Si:H/SiNx stack-layer films are piepared by plasm-enhanced chemical vapor deposition to passivate crystalline silicon solar cells. Effective lifetime of minority carrier is used to characterize their passivation property and the passivation mechanism is analyzed by simulating the high-frequency capacitance-voltage curves. It is found that compared to -Si:H films prepared by the same method, -Si:H/SiNx films show better passivation property. Through thermal treatment at different temperatures, the passivation property of -Si:H/SiNx films is improved to the best at 300 ℃ first, and then degraded with rising temperature. Annealing at 300 ℃ can make -Si:H/SiNx films show a better passivation property than -Si:H films in 90 min. Simulation results indicate that the passivation property of -Si:H/SiNx films is mainly determined by the state density at the -Si:H/Si interface.