Using Ni and Mo as active components and Al₂O₃?USY as support material, the effect of citric acid on the catalytic activity of NiMoP was investigated. The results indicate that the total acid content on the surface of catalyst increases at first and reaches its maximum in the condition of n_L/n_Ni=1.0, then decreases as the increasing concentration of citric acid. Meanwhile, the stacking layer number of active phase MoS₂ and the average lamellar length are gradually increased. When the mole ratio of citric acid to Ni is 1.0(n_L/n_Ni=1.0), the catalyst shows the best activity. And the HDS and HDN rate at 340 ℃ reach to 99.6% and 99.7% respectively, which are better than the catalyst without modifying by citric acid.