The physical and mechanical properties will be changed after being polluted and can be substantially influenced by the initial conditions of soil. According to laboratory experiments, different initial conditions including water content, particle and mineral constitutions, were considered to analyze the changes of soil properties pre and after being contaminated by heavy metal pollutants and oil pollutant. The results were as follows: 1) as the increase of initial water content, the density of silty clay pre and after polluted all increased. When the water content is lower than optimal water content (w_op), the relative change rate of density between polluted and unpolluted soil is much higher. 2) The plastic limit increased while the liquid limit decreased with the increase of water content within the range of lower than w_op. The variations were just opposite when the initial contents are higher than w_op. 3) The compressive coefficients as well as the relative change rate of polluted and unpolluted silty soils were all increased with the increment of water content. 4) the cohesion of uncontaminated silty clay was reduced as the increment of water content, while after being polluted, it was decreased within lower water content and then increased in higher water content. The inter friction angle of all kinds of polluted or unpolluted silty clay shared the variations of reduction as the water content increased, but with a different change rate in different range. 5) the composition of particle and minerals in soils are also significantly affect the change of properties being polluted. In general, cohesionless soil with higher particles and more primary minerals are more stable than cohesive soil under the same water content and pollutants.