This study presents the dynamic model for an industrial Universal Oil Product (UOP) fluid catalytic cracking unit on basis of mass and energy balance and the transfer functions are found. The riser and regenerator are simulated by using Matlab/Simulink software. The dynamic behaviour of the process is carried out by measuring the temperature response of the riser and regenerator to step change in gas oil flow rate, gas oil temperature, catalyst flow rate, air flow rate and air temperature. The simulator is validated by comparing the steady-state behaviour of the system with those in the literature and plant data and the results are found to be in good agreement. The results of simulation show that the process is strongly influenced by the catalyst flow rate, and any increase in the amount of coke on the catalyst and regenerator temperature would be compensated by a larger rate of consumption of the oxygen.