Efficient removal of chlorinated volatile organic compounds (CVOCs) has received great attention because of the considerable harm that they cause to the environment and to human health. Developing novel catalysts and exploring the catalytic activation and deconstruction mechanism of CVOCs molecule are always the focus in this field. Here, a set of Sn doped TiO2 catalysts were investigated for the decomposition of dichloromethane (DCM). Rietveld refinement of the XRD patterns showed that Sn ions can uniformly disperse into TiO2 and induce the crystal transition of anatase. Meanwhile, such decorating can induce an increase in specific surface area and affect the surface oxygen vacancy concentration of these samples, which have been demonstrated by N-2 adsorption and XPS, respectively. Catalytic performance tests indicated that the Sn0.2Ti0.8O2 has the best activity for DCM decomposition, and a lower CH3Cl selectivity than that of pure TiO2. Computational results suggested the dominant surface (110) of rutile Sn0.2Ti0.8O2 is more beneficial for the adsorption/dissociation of DCM molecule than that of anatase TiO2 (101). That's because the anchoring of DCM to Sn sites and electron enrichment on the surface bridge oxygen atoms of rutile Sn0.2Ti0.8O2 (110) can promote the nucleophilic substitution process for breaking of C-Cl bonds.