Numerous studies have demonstrated that the in-situ capture of arsenic by CaO is a promising approach to control arsenic emission from coal-fired flue gas at low and medium temperature. However, the actual temperature of flue gas in furnace exceeds 1000 °C and the reaction mechanism regarding capture of arsenic by CaO at such high temperatures is still unclear. Therefore, in the study, the interaction between arsenic in the vapor phase (As₂O₃(g)) and CaO in the simulated flue gas from 1000 to 1300 °C were investigated. The results indicated that the amount of arsenic captured by CaO increased with the increasing temperature and As₂O₃(g) was fixed into the products in the form of Ca₃(AsO₄)₂. Due to the formation of CaSO₄ in flue gas, SO₂ can significantly promote the adsorption of arsenic between 1000 °C and 1200 °C. However, with the increase of temperature, this promotion effect gradually faded or even disappeared. On the other hand, in the presence of NO, the slight inhibiting effect on arsenic capture occurred over almost the entire operating temperature range. It was also found that lattice oxygen could also be served as oxidant for the chemical oxidation of As₂O₃(g) in the absence of O₂. The results in this study suggested that the retention of arsenic from coal combustion flue gas in furnace could be facilitated by increasing temperature as well as O₂ concentration and usage amount of high-sulfur coal appropriately.