The fluid catalytic cracking (FCC) process continues to play a key role in a refinery . The FCC is one of the most energy consuming processes from the refinery, especially because of the fractionator. Therefore, the goal of increasing the efficiency and the economical benefits may be achieved through continuously improving of the energy consumption and FCC operation. The results of a previous work  - a case study using real data from a FCC plant presently exploited in a Romanian refinery - confirmed that it is possible to save energy from the FCC plant by adding new heat exchangers, re-piping, and improving the performance of the existing heat exchangers. The investigation of the entire heat integrated FCC plant behavior has not been studied yet. Nevertheless, this kind of studies is subjected to the high complexity of a FCC process. Moreover, the thermal integration of a process may induce more instability in its operation ; consequently a parametric sensitivity analysis was necessary to be used in this work in order to study the influence of different operating parameters values on the behavior of the retrofitted heat integrated design of the FCC plant. The Aspen Plus has been used to create the model of the integrated FCC plant. The simulations revealed a strong nonlinearity of the FCC process , affecting the products separation efficiency, and identifying the behavior of the integrated plant under the presence of different kind of disturbances.