A novel passivation technology of porous silicon (PS) surface, i.e., depositing diamond film on the PS surface by microwave plasma assisted chemical vapor deposition (MPCVD) method, was developed. The morphologies, structure and photoluminescence (PL) of porous silicon and diamond film were characterized using atomic force microscopy, scanning electron microscopy, X-ray diffraction, Raman spectrometer and PL spectrometer. The results indicated that the homogeneous and dense diamond film could be obtained by MPCVD method on PS, which stabilized greatly the luminescent wavelength and intensity, and moreover enhanced the mechanical strength of PS.