•We studied the effect of time on the characteristics of passive film formed on 316SS.•Both the film thickness and film resistance increase with time.•The increase of film thickness and resistance follows the direct logarithmic law.•The carriers’ density of the inner and outer layer of film both increase with time.•The increase of carriers’ density is related to the distribution of FeOOH. By potentiostatic polarisation for different time, passive films were formed on AISI 316SS. Characteristics of these films were studied using electrochemical measurement and surface analysis method. The results show the film thickness, film resistance and carriers’ density in the film all increase with time, and the increase of the film thickness and resistance both follows the direct logarithmic law. As time prolongs, FeOOH penetrates deep into the film, and its concentration in the film also increases, while the distribution of the other components of the film changes a little. The changing mechanisms of passive film characteristics with time were analysed.