Introduction  The heater’s terminal temperature difference is one of the main reasons that affect the heat economy of the unit. It has great significance to accurately and quantitatively calculate the effect of heater’s terminal temperature difference on heat economy.

  Method  A 660 MW unit was taken as the research object，the equivalent heat drop method was used to calculate the effect of the heater’s terminal temperature difference on the heat rate under the four operating conditions of THA， 80% THA， 60% THA and 40% THA. The influence of the terminal temperature difference of the same stage heater on the heat rate under different working conditions and its changing law were analyzed.

  Result  The results showed that the terminal temperature difference of the last stage high pressure heater and No.2 low pressure heater have a greater influence on the heat rate under various operating conditions. As the output of the unit increases，the effect of the terminal temperature difference of the same stage of high pressure heater on the heat rate gradually becomes larger， and the effect of the terminal temperature difference of the same stage of low pressure heater on the heat rate gradually becomes smaller.

  Conclusion  The research results are helpful for guiding the actual operation of the unit and improving the thermal economy of the unit.