Under the external loads, the volume of soft clay decreases with the time and several subsidence phases could be classified with the during development characteristics. And the compression indicators should develop gradually. With the soft clay samples taken from representative soft base before and after geotechnical process in some express highway area of the Pearl River delta, indoor consolidation tests were carried out under different pressure levels. With the data analysis, quantitative relation formulas were obtained for the compression modulus of silt soil with pressure and time. Consequently, dynamic evolution pattern of compression modulus was obtained.