Abstract: Lightly oxidized porous silicon was prepared by anodizing p-type single crystal silicon and photochemically oxidizing porous silicon.By means of SEM,AFM,FT-IR,the structure and morphology of the porous silicon was analyzed.The sensing performance was studied quantitatively by photoluminescence quenching of porous silicon.The results showed the structure of freshly etched porous silicon was very unstable because the silicon hydride (Si-H_x) on the porous silicon surface reacted with the ambient air easily.SEM images showed that the surface of the fresh porous silicon was covered by a lot of 120×40 μm rectangle pieces.After being oxidized by photochemical method,these rectangle pieces beceme smaller.AFM images indicated the porous silicon was covered by some porous silicon columns,and after being oxidized by photochemical method,the height of the columns decreased from 700~750 nm to 300~350 nm,and the thickness of the porous film was cut down from 50~58 nm to 40 nm;and partial Si-H_x band was replaced by Si-O band at around 1 114 cm^-1 and OSi-H band at around 2 249 cm^-1.The sensing experiment showed the photoluminescence of the stabilized porous silicon could be reversibly quenched by sulfur dioxide of different concentrations of,and the corresponding peak wavelength was not changed.