At present, there is very limited research on dynamic modeling of gas-steam combined cycle power plant (CCPP) units domestically, and the commonly used power system simulation software still lack CCPP models, to build a CCPP units model based on the characteristics of the domestic 9F heavy duty CCPP units with unfired heat recovery steam generator, single shaft and sliding pressure control, a real time digital simulation model of CCPP units is established. Firstly a non-real-time digital simulation model is established in the Matlab/Simulink environment, and then the model is converted into C language code. Secondly by using CBuilder, C language code is encapsulated in a simulation model which can run in real time. Finally the model is tested on Real Time Digital Simulator (RTDS), and verified with the field test results, which demonstrates that the developed CCPP model can meet the real time simulation requirements of power system in terms of computation efficiency and model accuracy.