Doosan Heavy Industries & Construction is developing a large-capacity industrial gas turbinewhich has large capacity of 270MW in power and competitive thermal efficiency over 40% and this study is about the result of the steady state performance analysis of the gas turbine under development.Currently, combined cycle power generation in Korea is taking the peak load area as a advantage of quick start/stop of gas turbine. Therefore, it is very important to understand and improve the part load operation performance characteristics of the gas turbine.In this paper, we evaluate the part load performance based on the characteristics of the components of the gas turbine being developed and further improve the part load performance through IGV control.