A calculating formula of compression strength for cement-stabilized soil in different sample sizes ratio of height to width (or ratio of height to radius) and surface frictional forces has been derived by twin shear stress yield criterion. The calculation results with the formula are farely coincide with the experimental ones. It is showed that the sample sizes and surface frictional forces influence the compression strengths. The bigger ratio of height to width (or radius) of the sample is

the less is its compression strength. The compression strength of the cement-stabilized soil sample putted on oil is lower than the no oil putted on it.