This study describes the particular development and investigation of a static and dynamic simulation model and its application to improve the start-up process of a combined cycle power plant. Generally, the power plant system and control design mean highly complex interactivities. The dynamic simulation models using powerful computers are effective tools for studying and understanding the operating characteristics of power plants to meet and improve the design, control strategy and operational requirements. The heat recovery steam generator (HRSG) is modeled by using commercial simulation software named advanced process simulation software (APROS). The HRSG model includes an advanced control philosophy and turbine bypass systems to have a high level of accuracy, especially during hard transients. The comparison between the simulation results and measured data is documented. The received results proved and embodied that the simulation is both very reliable to estimate the real HRSG dynamic behaviour and capable to predict the operational processes. Through a parametric study, the start-up time will be reduced while keeping the life-time consumption of critically stressed components under control. (C) 2008 Elsevier Ltd. All rights reserved.