In order to increase the overall efficiency of IGCC. integration of the steam-side subsystem in IGCC is attracting more and more attention with the development of technology and experience achievement. The existing design methods are generally the simulation and analysis of their performance under the conditions of the given steam subsystem configuration. This usually results in only partial optimization. In this paper, a new idea is presented and a new method-simultaneous optimization of configuration and parameters-is investigated and used for IGCC steam subsystem. These are expected to overcome the shortcomings of the previous ones, adapt to various IGCC technological demand for steam subsystem and realize better cascade utilization of exhaust heat from gas turbine. The optimization model for steam subsystem is established. based on modular modeling idea of general system integration. Case study shows that the synthesis optimization method and model presented in this paper are valuable for steam subsystem performance analysis and optimization design of IGCC.