The load of consumer demand is constantly changing. Therefore, controlling the generating units is the first issue for designing the power systems. In this paper, the steam generation unit and hydraulic generation unit are studied and simulated. The steam turbine has a re-heater and the hydraulic turbine has a transient droop compensation. The linearized math-ematical models of the first-order system of two generating units are expressed in the state space. The transient dynamic behavior of two generating units is investigated and com-pared with small changes in load demand. Also, the transfer function of the ratio of fre-quency deviation which changes with the changes in the load demand is shown for each unit. MATLAB software is used for simulation.