This paper presents a performance of a 300 kW Solid Oxide Fuel Cell Gas Turbine (SOFC-GT) pilot power plant simulator under an area of selection of the Proportional Integral Derivative (PID) controller coefficients that satisfies the stability, gain and phase margins. The performance of turbine speed and the fuel cell mass flow rate is controlled by the set of PID controller coefficients from this area. The input to the subsystems power plant are the electric load and cold air valve. The decentralized controllers are designed for each subsystems performance individually as a Single Input Single Output (SISO) system. Two of subsystem plants are the transfer functions of turbine speed over the electric load and the cold air valve. The other two subsystem plants are the transfer functions of fuel cell mass flow rate over the electric load and the cold air bypass valve. The flexibility to have an area to select PID controller coefficients is beneficial to SOFC-GT plant due to the wide range of operations and internal parameter interactions. Designing the PID controller for the specific phase and gain margins increase the reliability and robustness of the SOFC-GT with multiple uncertain parameters. The practical implementation of this methodology is presented through the software environment.