A new fuzzy evaluation method based on covariance index was proposed for performance of coordination control system in thermal power units.This method adopts the covariance benchmark index based on historical data

it takes the ratio of evaluation function of the benchmark data to the monitoring data as the control system performance evaluation index.Moreover

this method uses membership function to improve the judgment criterion of the covariance index

and the qualitative evaluation is turned into quantitative evaluation.Finally

the model simulation data and the industrial field data are used to verify the effectiveness of this evaluation method.