Combined cycle power generation is currently the most promising technology to generate power at higher plant efficiencies. In this study a simulation system program is proposed for simulation of pressurized fluidized bed gasification and combustion based combined cycle power generation unit, utilizing Turkish lignite as a fuel. The effect of pressure ratio, gas turbine inlet temperature, gasifier carbon conversion and the bottoming steam cycle configuration, on the plant performance, for the unit is investigated. System data of the Texaco gasifier and the related plant (coal preparation, air separation unit, circulating fluidized bed, gas cleaning, gas turbine, steam turbine and the heat recovery steam generator) are considered. By steps of 5% increase of overall pressure ratio affects the net power, gas turbine power and steam turbine power increases about 0.63%, 7.65% and 0.32%, respectively. Gas turbine inlet temperature is increase from 1150 to 1200 degrees C, net power output, gas turbine power output and steam turbine power output increases about 1.42%, 4.0% and 0.22%, respectively. Steam turbine pressure is increased between 70 and 110 bar in step of 10bar; net power output increase about 0.90%, gas turbine power output increase also by 0.50% and steam turbine power output increased about 0.25%. Increase of gasifier carbon conversion affects the net power and net electric efficiency about average increase of 0.03% and 0.063%, respectively. In this case, the optimum output work is considered by increasing the pressure ratio, gas turbine inlet pressure, steam turbine (ST1) inlet pressure, HRSG superheated outlet temperature and higher gasifier carbon conversion.