Pyrolysis gasoline is one of the by-products in the pyrolysis of hydrocarbons to produce ethylene. In industrial production, unsaturated groups of benzene ring branched chains in pyrolysis gasoline are usually saturated by two-stage adiabatic fixed bed catalytic hydrogenation. The first-stage hydrogenation mainly saturates dienyl groups such as conjugated dienyl under low-temperature liquid phase conditions, and the second-stage hydrogenation saturates monoenyl groups under high temperature. According to the removal sequence of C₅ components, pyrolysis gasoline hydrogenation unit can be divided into front-end depentanization and back-end depentanization, namely middle distillate hydrogenation and full hydrogenation. At present, most chemical enterprises adopt front-end depentanization, while some enterprises use back-end depentanization. In this paper, the factors influencing the operating cycle of second-stage catalysts in full hydrogenation unit of pyrolysis gasoline are analyzed, and some corresponding solutions are put forward.