Pygas hydrogenation unit and styrene extraction unit are mutually upstream and downstream, with raw materials and products supplied to each other and close operational connections. Based on the process optimization and system integration research on these two units, measures such as joint separation process, thermal coupling for distillation separation, joint hydrogenation reaction and joint utilities can be taken. After optimization, the joint design of pygas hydrogenation unit and styrene extraction unit is feasible in engineering and can achieve the goals of reducing the investment, saving the energy consumption, and improving the economic benefits and competitiveness of the units.