Abstract: With the development of industrialization and urbanization in China, the problem of soil (including expansive soil) contained acidic or alkaline industrial wastes produced in the industrial production processes is becoming more and more serious. In order to explore the swelling and shrinkage deformation law of natural expansive soil when subjected to acid or alkali solutions, 1-D compression and swelling tests were carried out, furthermore, microscopic mechanism of macroscopic volume behavior of expansive soil was revealed by microscopic test and chemical composition analysis of pore water. Experimental results showed that the micro-structure system of specimens is significantly altered after being subjected to acid and alkali solutions. Acid pollution has a dissolution effect on the mineral composition of the soil, resulting in an increase in the internal pores of the soil and an increase in the soil compressibility. Alkali pollution causes montmorillonite and illite in expansive soil to form cemented gel, resulting in flocculent micro-structure, reduced void ratio and reduced soil compressibility. In an acidic environment, H+ ions replace the exchangeable cations ( Na+, K+, Ca2+, etc. ) in clay minerals, resulting in an increase in the thickness of the diffusion double layer and an increase in soil expansion. In the alkaline environment, the cation exchange reaction occurs between Na+ ions and exchangeable cations such as Ca2+ and K+, the thickness of the diffusion double layer is reduced, and the soil expansion is weakened. Therefore, in the construction of acid or alkali contaminated expansive soil sites, the adverse effects of the deterioration of expansive soil engineering properties caused by acid or alkaline environmental pollution should be considered respectively.