Abstract: In this article, based on the heat balance diagram of 1 000 MW ultra-supercritical coal-fired unit, through calculating &analyzing the influence of HP heater superheated steam cooling section outlet design temperature on HP heater heat transfer area and HP heater upper terminal difference; and influence of HP heater terminal difference(upper/lower) on heat transfer area, unit heat consumption value, has presented the HP heater upper terminal difference should not be set to -2℃ according to the specification, but determined by calculation on specific project conditions, and has provided reference for energy conservation of power units.