The crude distillation unit performs the initial distillation of the crude oil into several boiling range fractions, and it is one of the most energy consuming and complex distillation columns in a refinery. The operational objectives are to maximize the yields of on specification distillates, increase crude capacity, reduce fuel consumption, maximize the heat recovery, stabilize the column operation, and enhance the operator's task. In order to resolve these objectives, the following works should be done simultaneously. They are rigorous process modeling, advanced process control, and optimization. The development procedure of the on-line optimization system is presented, and it is applied to the actual Exxon crude unit as an example. The rigorous process model is obtained by using the general purpose process simulator, ASPEN PLUS, and its results show close agreements with plant data. The advanced control scheme, QDMC, is applied and shows good control performance when compared with conventional decentralized control. Finally, the optimization studies under several sets of cost data are performed. The optimized operating conditions are calculated and their economic benefits are verified.