Abstract: A 3.2Mt/a hydrotreating unit after a long running cycle was evaluated. The operation performance of this running cycle was summarized and some suggestions were proposed. During this 1st running cycle, the average deactivation rate of catalyst was 0.026 ℃/d, the average rising rate of pressure drop in the 1st stage of reactor was 9.9×10-5 MPa/d and the scale resistance in the high pressure heat exchanger reached 1.2×10-3 m2.K/W by the end of this operation cycle. Based on the above data and the predicted values of catalyst service life, the rising rate of pressure drop in reactor, as well as the fouling in high pressure heat exchanger calculated by the modified deactivation model, it can say comprehensively that the next running cycle could be 1 417 days.