Abstract: The deep hydrofining catalyst FHUDS-6 was applied in a 4.1 Mt/a diesel hydrofining unit firstly, and the operation data of performance test in full capacity was analyzed. Results show that using a feedstock with 11% FCC diesel fraction, under the process conditions of an average catalyst bed temperature of 352 ℃, a space velocity of 2.53 h-1, a hydrogen partial pressure of 6.15 MPa and hydrogen to oil volume ratio of 254.3, FHUDS-6 catalyst exhibits high hydro-desulfurization activity and hydro-upgrading activity, the sulfur removal rate researches 98.02% and the cetane number of treated diesel fuel increases by 5.7 units. The quality of the obtained diesel product can meet the requirements of National Emission Standard III for diesel fuel.