Abstract: In order to make better use of catalysts in different reaction regions of diesel ultra deep hydrodesulfurization technology（RTS）, in which two reactors in series were adopted，grading schemes for Ni-Mo-W type catalyst with high hydrogenation activity，Co-Mo type catalyst with high direct desulfurization activity，and Ni-W type catalyst with slight hydro-upgrading activity were compared in the pilot plant. The results showed that the effect of graded catalysts system on ultra-deep hydrodesulfurization was comparable to that of Ni-Mo-W catalyst alone. If Ni-Mo-W type catalyst was used in the first reactor and Ni-W type catalyst in the second reactor，the density and polycyclic aromatic hydrocarbon content of the product was effectively reduced. If the first reactor used Ni-Mo-W type and Co-Mo type catalyst in equal volume，and Co-Mo type catalyst was used in the second reactor，the hydrogen consumption could be effectively reduced.

Key words: ultra low diesel, deep desulfurization, catalyst grading technology