The heavy metal arsenic and its compounds cause serious damage to human health because of their carcinogenicity and accumulation in natural environments such as groundwater. Cu-doped TiO2 catalyst was synthesized by impregnation-thermal decomposition method. The copper dopant induced the number of oxygen vacancies in titanium dioxide and increased the activity of oxygen molecules, which optimized the arsenic reaction pathway and improved the arsenic removal from desulfurization wastewater. The experimental results show that the Cu concentration was important factor affecting the arsenic removal of the composite material at atmospheric temperature (25 ℃) and pH=7, and the arsenic removal efficiency of CT10 reached 83.17%, which was 1.33 times higher than that of the original sample. Subsequently, the arsenic adsorption at different pH with optimal doping ratio was carried out to study the role of pH on modified catalysts, and it was found that the adsorption of arsenic by Cu/TiO2 was the best when pH=5. Characterization analysis further showed that Cu doping effectively increased the oxygen vacancies concentration for promote the activation of oxygen molecules, enhanced the chemisorption of As on Cu/TiO2 with high adsorption capacity for arsenic in wastewater. Combining the characterization and experimental results, the migration mechanism of arsenic from wastewater in Cu/TiO2 composite catalysts is proposed, and the mode of action of Cu doping in the substrate adsorbent is investigated. The density-functional theory (DFT) was employed to calculate the modified catalyst band gap, combined with simulations to analyze the mechanism of oxygen vacancies caused by ion doping. The outcome of this work provided reference for future coupling of transition metal ions with catalysts and a realistic technological pathway for the catalytic remediation of heavy metal pollution in wastewater.