Abstract: Using the light crude oil as material, the effect of theoretical stages of atmospheric column cleaning and steam stripping sectors and over-flash ratio on the separation of atmospheric light and heavy fractions were discussed respectively with PRO/II process flow simulation software. The suitable design conditions were determined. The results indicated that the optimal design conditions of the 2nd atmospheric and vacuum distillation unit atmospheric column in the PetroChina Karamay Petrochemical Co., Ltd. are the numbers of the cleaning section theoretic stages for 3, the numbers of the steam stripping section for 3 and the atmospheric column feed temperature for 360 ℃. After revamping, the atmospheric pull rate was significantly increased from 40 wt % to 44.81 wt %. The transformation effect was satisfactory.