Abstract: The existing atmospheric and vacuum unit of a refinery was simulated and analyzed, and the problems were found to be unsatisfactory total production, unequal pressure drop of heat exchange branches and heat exchange end temperature lower than design value. The model of the unit was set up with Aspen Plus software. By using intelligent graphical method, the effect of draw rate rate on product quality was investigated and optimized. The total production of the retrofit design was increased by 3.8%. Hydrodynamic rating of columns was performed. Based on simulation results, the cold and hot stream data were extracted for heat exchanger network synthesis, analysis and optimization with the intelligent graphical method by using the HENS software. The heat exchanger network end temperature of the retrofit design was increased to 288 ℃, 18 ℃ higher than exiting value. Five new exchangers with 1825 m2 were added in the retrofit. Compared with the primary network, the structure was modified only insignificantly.