Catalytic hydrochlorination of Si is an effective route to manufacture trichlorosilane (TCS), the main feedstock of high-purity Si for solar cells. However, the understanding of its catalytic process is still limited. Herein, we prepared CuO catalysts modified with Fe2O3 promoter (Fe2O3-CuO) by one-step hydrothermal method and investigated their catalytic performance for producing TCS. Compared with the non-catalytic case, pure CuO catalyst, and the Fe2O3-CuO-M catalyst obtained by mechanically mixing CuO with Fe2O3, the Fe2O3-CuO catalyst exhibits the highest TCS selectivity and Si conversion. The introduction of Fe2O3 facilitates lattice oxygen migration of CuO due to the electron interactions between Fe2O3 and CuO. During the reaction, CuO transforms into CuCl2 and CuCl2·2H2O, then to CuCl. The latter is the key intermediate for forming the active CuxSi phase. This work discloses the transformation of the CuO catalyst during the Si hydrochlorination reaction, and provides new insights into the catalytic mechanism.