The grid frequency is controlled cooperatively by the governor of the Turbine-Generator and the automatic generation controller(AGC) of the KPX(Korea Power Exchange). It is a basic requirement that the reliability of the governor is verified to enhance the power system stability but it is not easy to confirm the response characteristics of the governor because all generators are operated in the grid system that has the constant voltage and frequency. Therefore, it is necessary to study a new test method in order to examine the governor dynamic characteristic in the similar fault conditions. A study has shown that it is verified to simulate the turbine-generator power control system, the governor response characteristic under limited conditions and contribution of AGC with the gas turbine generator simulation model as well as demonstrate the dynamic response of the governor with the developed governor dynamic characteristic tester based on digital controller while the turbine-generator is connected to the grid system. This tester is constructed by the built-in functions of the turbine-generator main controller. In this treatise, the theoretical background, development method and the results of both simulations and demonstrations are described as another way to verify the turbine-generator governor dynamic characteristics.