This study simulates the transient behavior of a dual-pressure bottoming system for the combined cycle power plant. In order to set up a comprehensive model to represent the system effectively, unsteady one-dimensional conservation equations for each component are introduced. Controls over water level and turbine power are also incorporated in the simulation process. How the bottoming system responds to the varying conditions of the gas turbine exit was investigated. Two types of the bottoming cycle operation were simulated: a pure sliding-pressure operation (where the shaft power control is not performed) and a modified operation (where the shaft power is controlled to match a given load by modulating the steam flow rate). Variations in the main operating parameters for both low and high pressure levels were examined, and the transient characteristics of two operations were compared.