The thermodynamic characteristics of combined heat and power generation unit of gas-steam combined cycle under different working conditions are compared to find the location and causes of the unit heat loss. It can provide theoretical guidance for the optimal operation and energy-saving transformation of the unit. In this study

thermal efficiency of unit is calculated by the direct balance method of the heat method at first. Then exergy loss is calculated by the indirect balance method

and the calculation results are checked and analyzed with the results of direct balance method. Finally

the exergy analysis method is used to calculate the energy loss and efficiency of combined heat and power generation unit of gas-steam combined cycle. By comparing the results of the heat method and the exergy analysis method

it is found that

the increase of engine load has a great influence on heat loss and efficiency of the combined cycle

which improves the unit exergy efficiency. The exergy efficiency decreases slightly with rising ambient temperature. The changes in the exergy efficiency of gas turbine determine the trend of changes in unit exergy efficiency

and the use of combined heat and power generation unit can effectively improve the operating economics of the gas-steam combined cycle unit.