In order to improve the efficiency of a large number of subcritical units in service and accelerate the high-quality development of coal-fired power plants, the retrofit technology of raising temperature to 600 ℃ for subcritical units was carried out. According to the thermodynamic principle, the efficiency benefit of increasing steam pressure is obviously lower than that of raising steam temperature. Therefore, the steam temperature at the inlet of steam turbine of subcritical unit is increased from 537 ℃ to 600 ℃ under the condition of keeping the steam pressure (16.7 MPa) at the inlet of subcritical unit unchanged. After the main and reheat steam temperature rises to 600 ℃, the unit efficiency of a 320 MW subcritical unit (pure condensing without heating unit, back pressure of 4.9 kPa) can reach the level of ultra supercritical unit in service, and greatly improve the (ultra) low load performance of the unit. Under the rated condition, the power supply coal consumption can reach below 290 g/(kW·h).