The invention discloses a diesel oil deep hydrodesulfurization catalyst and a preparation method thereof. The catalyst comprises a carrier and a hydrogenation active component, the carrier is an inorganic refractory oxide with surface loaded with Ce1-xMxO2-delta, wherein M is one or more selected from Mn, Fe, Co, Ni, Cu, Zr, Nb, Bi and Sn; x is less than or equal to 0.98 and greater than or equal to 0.02; delta is greater than or equal to 0 and less than or equal to 0.5; the hydrogenation active components are Mo or/and W, by taking weight of the catalyst as a reference, Ce1-xMxO2-delta is 1.0-10%, by taking oxide as a reference, Mo or/and W is 2.0-30%. The preparation method comprises the following steps: 1) loading the Ce1-xMxO2-delta on the inorganic refractory oxide, performing drying and roasting; and 3) then dipping the hydrodesulfurization catalyst carrier in the solution containing the Mo or/and W hydrogenation active components, and performing drying and roasting to obtain the catalyst. The Ce1-xMxO2-delta composite oxide is loaded with the surface of the carrier, hydrodesulfurization capability of the catalyst is further enhanced, and the catalyst can be used for hydrodesulfurization of straight-run, catalysis, and coking or its mixing oil.