Abstract: Heat pump heating and back-pressure expander heating are two common schemes for cascade utilization of extraction steam for heating. However,the off-design characteristics of the two schemes are not clear,and there are few comparative studies between the two schemes. Through modeling for each equipment,taking a 300 MW cogeneration unit as an example,the thermodynamic performances of the two schemes under variable working conditions are analyzed. The results show that for the heat pump heating scheme,there is an optimal outlet temperature under different main steam flow rates corresponding to the lowest coal consumption rate of the system. The heat pump heating scheme with the optimal parameters is compared with the expander heating scheme,it is found that when the extraction steam parameters are low,the coal consumption rate of the heat pump heating scheme is higher than that of the expander heating scheme. With the increase of extraction steam parameters,when the optimal outlet temperature of the heat pump is higher than 70 ℃,the coal consumption of the heat pump heating scheme is lower than that of the expander heating scheme. Similarly,when the extraction steam parameters are low,the heating process exergy efficiency of heat pump heating scheme is lower than that of expander heating scheme. When the optimal outlet temperature of the heat pump exceeds 64 ℃,the heating process exergy efficiency of the heat pump heating scheme begins to exceed that of expander heating scheme. The equivalent energy saving index is proposed,and the calculation results show that the index can be used to compare the energy-saving benefits of the two schemes.