This work represents a mathematical analysis and simulation of dc-motor electric drive control system with variable moment of inertia. A separately-excited dc motor is used in this control system. A mathematical model for this motor has been simulated and tested in Matlab/Simulink. A closed-loop control system for this dc electric drive system is proposed. The proposed control system is based on the technical optimum method of design. The controlled variable of this system is the load angular speed. In this control system the moment of inertia is considered to be variable. It varies as a function of time. A speed controller and a current controller are designed for the suggested model to meet the desired performance specifications by using the technical optimum method. These controllers are attached to the control system and the closed-loop response is observed by simulation and testing this model. The results show the high-performance of the designed control system.