Heat recovery boiler is one of the part of combined cycle plant. It has key role in plant overall performance and efficiency. Heat recovery boiler get into trouble in effect of the false designing or time lapse . these trouble is: fouling on the tubes bundle, corrosion, vibration in the tubes bundle, and pressure drop of the output smoke on heat surfaces. One of the important trouble is pressure drop of the output smoke in the gas turbine. It will disturb gas turbine operation and disrated efficiency. In beginning of this project, inlet duct of heat recovery boiler is simulated with fluent software, and some suggested guide baffle was used in the output for flow integration. Number and distance was defined with trial and error for better integration of flow and pressure drop was calculated on the several sample of tubes bundle of different cross section with different layout, finless and fin tubes( with several common fin and suggested), and results was compare with each other. This results was achieved that fin tubes bundle with U helical fin was the best. Pressure drop of some tubes bundle was calculated with experimental relations, good match was observed between results of the simulation and experimental relations. Key words: combined cycle plant, heat recovery boiler, pressure drop, vibration, baffle, heat surface.