Abstract: For an ultra-supercritical unit with a back pressure steam turbine for heat supply, researches were conducted on the unit with deep peak regulation under different heat supply modes. Through theoretical calculations, the economic benefits of the back pressure turbine under operational and non-operational modes during deep peak regulation conditions were analysed, while comparisons and analyses were conducted on the economic benefits of the steam from the back pressure turbine for the regenerative heating system and directly for external heat supply. Result show that the comprehensive economic benefit of the back pressure turbine under operational mode in low load is increased by 198 400 yuan per year compared with under non-operational mode. The unit heat rate of the back pressure turbine for the regenerative heating system is improved by 171.83 kJ/(kW·h) under 50% load compared with directly for external heat supply.Under deep peak regulation condition, the method of the back pressure turbine directly for external heat supply can be adopted when the flow rate for heat supply is higher than the minimum flow rate at the back pressure turbine inlet, and the method of the back pressure turbine for the regenerative heating system can be adopted when the flow rate for heat supply is lower than the minimum flow rate at the back pressure turbine inlet. Finally, the flexibility of unit operation can be improved with the back pressure turbine put into operation under deep peak regulation condition.