In the analysis of thermal economic benefit of modern large thermal power plant, in order to accurately determine the performance and energy consumption of steam turbine unit, the measurement of boiler main feed water and condensate flow rate is effectively controlled. When the test was conducted in accordance with ASME PTC6 standard, the precision calibration of the main condensate flow rate and condensate flow rate reached 0.25%, and the proportional relationship of the measured value on the accuracy of the calculation result of steam turbine heat consumption rate was about 1:1. In the modernization transformation of large steam turbine set, the examination of cylinder interior can reflect the transformation effect, so the main condensate water measurement has a greater impact on cylinder efficiency. According to ASME standard, high-precision differential pressure element is used for flow measurement, which makes ASME throat pressure nozzle more and more popular in engineering application. Recommended by the American society of mechanical engineers (ASME), its superior performance has been widely recognized internationally, in many places requiring high precision flow measurement, ASME PCT6 nozzle has become the preferred solution.