Fluid Catalytic Cracking Unit (FCCU) is an important processing unit in an oil refinery. Fluid catalytic cracking is a process used to convert heavy petroleum products to light products such as gasoline, light fuel oil, and petroleum gas. In the fluid catalytic cracking reactor, heavy gas oil is cracked into more valuable lighter hydrocarbon products. The reactor input (the gas oil feed to the reactor) is a mixture of hydrocarbons that makes the reaction kinetics very complicated due to the involved reactions. The process is highly nonlinear and multi variable with severe interactions. For the simulated dynamic model of FCCU plugged with yield model, sensitivity studies has been carried out to study the effects of independent variables such as feed preheat temperature, feed flow rate and air flow rate in maximizing gasoline yield. With the optimized model, the closed loop studies have been carried out for reactor and regenerator temperature control of FCCU with minimum overshoot as the performance criteria.