Abstract: This paper presents a united expression of the compression lines of normal compressed clay, overconsolidated clay and sand by introducing a special vertical stress in single logarithmic coordinates. And then, based on the new expression and the concept of compression modulus, we obtain a calculation method for the compressive modulus of soil. Evolutionary laws of compressive modulus are presented and analyzed with the special vertical stress and compression index changing, respectively. Finally, comparisons with the test results and foundation settlement in engineering case indicate the rationality of this calculation method.