The delayed coking unit in Khartoum Refinery is using cascade control technique for controlling the bottom level of the Coker fractionator, A temperature in the stripping section is held by steam to the reboiler. Situation may arise where the base level continues to drop even with the valve of the bottom flow is fully closed, this is due to the fact that the boil rate is greater than the liquid condensation rate which means that the rate of the steam to the reboiler is very high. It is required to control this critical situation by cascade control technique. MATLAB tool box consider as the main software used in the analysis the control loop of the delayed coking unit . The graphical user inter-phase (GUI) tool box helps in obtaining the transfer function for the coker fractionator which leads to complete analysis using Simulink in continuous, frequency domain and digital system. Unit Step applied to the transfer function which results in finding the final value = -0.02, the offset = -1.02 and settling time =7.71 sec. Different tuning methods were applied for the system to find the ultimate gain and Ziegler-Nichol table used for the recommended values. The roots locus method is preferable compared to other methods for the least deviation from the a average values which results in Kc=0.15,τI=1.3335min, τD =0.33 min