Abstract: Using high back pressure heating mode for large steam turbine units can make full use of waste heat of exhaust steam and improve fuel utilization efficiency. Thus, more and more thermal plants have carried out high back pressure heating transformation. In order to ensure the operation economy of high back pressure unit, Ebsilon model was established for 330 MW high back pressure cogeneration unit to conduct simulation under all working conditions. Secondly, we calculated the theoretical load range of the unit according to the minimum cooling mass flow of LP cylinder and established the mathematical model of the heat supply network according to its actual heat load conditions. Then, combined with the supply and return water temperature of heat supply network, we analyzed the back pressure operation mode and electric load range at different ambient temperatures and determined the actual operation boundary of the unit after the optimization of back pressure. We analyzed the economy of the return water of heat supply network deviating from the ideal value to determine the high back pressure operation strategy of the unit. Results show that the high back pressure waste heat of exhausted steam heating mode can improve the heating capacity by about 80 MW, but its environmental temperature adaptability is poor. When the ambient temperature is high, the economy of high back pressure heating is better than that of extraction condensate mode. The optimized back pressure operation mode can reduce the coal consumption of standard power generation by about 34 g/kW·h. In addition, the return water temperature of heat supply network seriously affects the economy of high back pressure units: at different water supply temperatures, the return water temperature of boundary of high back pressure operation changes accordingly.