A series of Ni-Mo-W slurry catalysts were prepared by a novel complete liquid-phase method and tested for diesel ultradeep hydrodesulfurization (HDS) in a slurry bed reactor. Results showed that Ni-Mo-W catalysts prepared by this novel method exhibited a relatively high HDS efficiency, reaching approximately 96%. Characterization results showed that a suitable amount of W was beneficial for the dispersion of MoS2 species and the production of small particles. Meanwhile, the catalysts incorporating a suitable amount of W had a shorter slab length and more stacking number of MS2, which would enhance the HDS activity. It was also found that HDS efficiency was closely related to (Ni + Mo + W)/(Ti + Al) atomic ratios on the catalyst surface. The incorporation of a suitable amount of W was beneficial for the HDS reproduction, and the best catalytic performance was obtained when the Ni/W atomic ratio was 1:0.5.