The synergism of promoter Co on the performance of MoS2 phase in selective hydrodesulfurization (HDS) of FCC gasoline was studied by regulating the step impregnation-sulfurization sequence of Co and Mo species to adjust the proportion of Co-Mo-S phase, separated Co9S8 and MoS2 phases. The evaluation results demonstrated that the CoMo/gamma-Al2O3 catalyst with Co species first impregnation-sulfurization showed higher HDS activity and selectivity. The characterization by XRD, HRTEM, XPS, TPR and FT-IR showed that, on this catalyst, the interaction between the sulfurized Co and MoS2 phases was weak, and lead to the lower Co decoration on the MoS2 phase, thus forming more Co9S8 phase. The more formed Co9S8 phase could produce more hydrogen spillover (Hso) to create more CUS and SH groups, thus greatly improving the HDS activity and selectivity. Through the layered loading test of Co9S8/gamma-Al2O3 and MoS2/gamma-Al2O3 catalysts, it was found that the Hso synergetic effect between the Co9S8 and MoS2 phases could significantly improve the HDS activity, but showed very little effect on the saturation of olefins. (C) 2016 Published by Elsevier B.V.