In order to meet the requirements of depth peak regulation and heat supply of the power grid, the low pressure cylinder needs to operate under low load or even zero output conditions for a long time. In this paper, a 660 MW steam turbine is taken as an object to study the flow characteristics and operation safety of lowpressure blade under deep peak load and heating conditions. The flow field distribution of lowpressure last stage blade under different exhaust pressures and the law of the change of related parameters with back pressure are obtained. The bending stress of the blade subjected to steam flow is analyzed and calculated, and the change of the bending stress with back pressure is determined. The results show that the steam flow bending stress of the blade is very small under the condition of deep peak regulation and small volume flow of heat supply, which can meet the design requirements of the blade without frequency modulation and ensure the safe and stable operation of the unit; under the condition of small volume flow rate, the exhaust pressure of the turbine is reduced, the vacuum degree is increased, the friction blast loss of the low pressure part is greatly reduced, the problem of blast heating is reduced, the bending stress of the steam flow is reduced, and the steam turbine can operate safely and stably.