Taking a 1000MW ultrasupercritical unit as the research object, the transformation of the unit without economizer was studied. The boiler, turbine and thermal system of the power plant were considered as a whole. A highpressure heater was added to the unit. The flow rate of the unit was changed and as a result, the heat absorption of the boiler heating surface was also changed. The heat regenerative system was optimized. The results have shown that the exergy efficiency of the boiler increased from 54.0% to 54.4%. Standard coal consumption rate of power supply is reduced from 304 g/kWh to 302.9 g/kWh.