Sn-based compounds are typical promoters for Cu-based catalysts used in the Rochow-Müller reaction, which manufactures most organosilicon monomers in the industry. However, the role of these promoters and the detailed structural evolution of Cu-based catalysts during the reaction have not been clearly clarified in the literature. Herein, a series of SnO2-modified commercial Cu2O catalysts (xSnO2/Cu2O, x = 0.01, 0.03, and 0.1) with different SnO2 contents (0.01, 0.03, and 0.1wt%) were prepared and tested for the Rochow-Müller reaction. Among these catalysts, 0.03SnO2/Cu2O exhibits the highest dimethyldichlorosilane selectivity of 87.8 % and Si conversion of 35.8 % at 325 oC. The detailed characterization and analysis reveal that introducing SnO2 promotes the transformation of Cu2O to CuCl and Cu and further to the active Cu3Si phase, thus leading to the high catalytic performance of the SnO2-modified Cu2O catalysts. This work provides new insights into the SnO2 promotion to the Cu-based catalysts and the catalytic mechanism in the Rochow-Müller reaction.