Abstract: Cold high-pressure separation process is now widely used in isomerization unit of PX complex, and results in an unreasonable energy consumption of PX complex. The advantages and the problems when using hot high-pressure separation process are analyzed. An accurate method for determination of isomerization product distribution is established. The hot high-pressure separation process is simulated by ASPEN PLUS, and the results indicate that recycle hydrogen concentration is almost not changed, compared with cold high-pressure separation process. Hot high-pressure separation process is proved to be feasible by industrial practice. The energy optimization scheme is proposed, and the simulation proves that the energy consumption of 370 kt/a PX complex can be reduced by 627 MJ/t.