Abstract: Childs and Collis-George(1950)proposed a model for predicting the coefficient of permeability based on the random variation of pore size.It was then improved several times and proved to be effective.Based on this model,the relative coefficients of permeability of Shanghai soft soil were predicted from the soil-water characteristic curves.It was shown that permeability parameter of Shanghai soft soil varied nonlinearly with suction(water content),and it decreased quickly with increasing of suction(decreasing of water content).For different grain sizes of Shanghai soft soil,at the beginning of de-saturation(low suctions),the size of soil grains had little influence on permeability.But with the progress of de-saturation,the decreasing rate of permeability of large grain soil was larger than that of small grain soil.At the last stage of de-saturation,the difference of the decreasing rate became unobtrusive.This decreasing phenomenon was mainly related to the character of water that participated in the process of de-saturation.