Abstract: The running of a 4.1 Mt/a diesel hydrogenation unit with deep desulfurization catalyst for quality upgrading was introduced. In the diesel quality upgrading process, the deactivation speed of catalyst became faster and the Si in coker gasoline made catalyst poisoned. In the mean while, the balance of diesel cetane number was broken. To solve above problems, the following countermeasures could be taken. Firstly, the space velocity should be decreased. Secondly, the Si content in coker gasoline should be controlled. Thirdly, the diesel cetane balance of the refinery plant should be optimized.