Abstract: Taking 9 FB combined cycle unit as a case study, the mathematical model of main components was established and the overall calculation model of the combined cycle unit was obtained. Aiming at the heating mode of adjustable extraction or back pressure and the driving mode of two-on-one or one-on-one, the unit thermodynamic performance is analyzed to obtain the power and heat load characteristics under variable operating conditions. The unit operation mode was optimized to obtain the adjustable range of electric load in different heating periods and the thermal economy in peaking operation was studied. The results indicate that when heat load is low at the beginning or end of heating period, the unit had better be in coordination of two-on-one adjustable extraction mode and one-on-one back pressure mode, and the peaking capacity ratio is 52.6%～53.4%. When the heating load gets higher, the unit had better be in coordination of two-on-one adjust extraction mode and two-on-one back pressure mode, the peaking capacity ratio is 44.5% ～ 55.4% at cold period, and 27.4%～33.5% at the coldest period in order to ensure the demand of heating. After optimization, the flexibility of combined cycle heating unit in the whole heating season is significantly improved, which could provide 1.176 billion kW·h for renewable energy.