Method for online monitoring performance of steam turbine of coal-firing unit

The invention provides a method for online monitoring performance of a steam turbine of a coal-firing unit. The method includes the following steps: step 1, according to boiler operation designing procedures, acquiring boiler structure parameters, and reading real-time data of operation condition measuring points of a steam-water system and a heat exchanger system at a given moment from a real-time database of a DCS (distributed control system); step 2, calculating specific enthalpy and density of a working medium on the basis of a working medium physical parameter library; step 3, according to a working medium side energy balance model, respectively calculating heat absorbed by the working medium in the steam-water system and the heat exchanger system to acquire total energy increment of the working medium; step 4, building a transmission function model between the total energy increment of the working medium and output power of the unit, and acquiring efficiency and heat consumption rate of the steam turbin