Abstract: The theoretical analysis shows that fractional differentials can greatly increase high frequency,reinforce medium frequency and non-linearly preserve low frequency of signals,hence they could be used for edge and texture enhancement as well as smooth area preservation.In this work,from classical fractional differential G-L definition,fractional order differential difference function is derived and an approximate fractional order differential Tiansi module is constructed.Experimental results show that image enhancement methods based on fractional differential are markedly superior to those based on integer differential in visual effects.