The energy-intensive hydrotreating processes, which operate at high pressure and high temperature, are widely adopted in refineries to improve the quality of oil products. In this paper, the energy and emission performance of a vacuum gas oil hydrotreating unit is investigated by the exergy load distribution analysis incorporated with process simulations. The quantitative relationship among the exergy loads, exergy efficiencies of the subsystems and the exergy efficiency of the entire system is obtained. Two operational optimisation strategies and one retrofit scheme for the entire system are proposed by adjusting the exergy loads and exergy efficiencies of the subsystems. Results show that the exergy efficiency of the entire system increases by 1.23% through the proposed operational optimisation strategies, and the CO2 emission of the entire system can be reduced by 56.45% through the proposed retrofit scheme.