Studies on the passivation of monocrystalline silicon wafers by using plasma enhanced chemical vapor deposition for the deposition of monolayer intrinsic hydrogenated amorphous silicon films show that increasing the hydrogen dilution ratio is beneficial to reducing the defects in the films and enhancing the passivation effect. Excessive hydrogen dilution ratio can lead to the epitaxial growth of amorphous silicon on the silicon wafer surface and reduce the passivation effect. Annealing results in the increase of the degree of crystallization of amorphous silicon and the reduce of passivation effect. Meanwhile， annealing improves the quality of thin films and changes the way of H bonding and enhances the passivation effect. Therefore， the best passivation effect of monolayer hydrogenated amorphous silicon can be obtained only at appropriate hydrogen dilution ratio and annealing temperature. In order to improve the passivation effect of amorphous silicon film on silicon wafer， tandem intrinsic amorphous silicon film with high and low hydrogen dilution ratio is used to passivate silicon wafer. Therefore， the epitaxial growth of amorphous silicon on the silicon wafer surface can be avoided by stacking amorphous silicon thin films with high hydrogen dilution ratio on the thin films with low hydrogen dilution ratio. In the annealing process， the hydrogen in the film with high hydrogen dilution ratio diffuses into the film with low hydrogen dilution ratio， effectively passivating the suspension bonds on the surface of amorphous silicon and monocrystalline silicon， and improving the interface quality of amorphous silicon/silicon wafer. After the tandem passivation of the silicon wafer， the effective minority carrier lifetime is 7.36 ms， and the implied open-circuit voltage is 732 mV.