The invention discloses a method for evaluating the data quality of a PMU (Phasor Measurement Unit) and estimating the angle error of the PMU by utilizing difference comparison between measured data of an RTU (Remote Terminal Unit) and the data of the PMU, belonging to the technical field of automation of a power system and solving the problem of evaluation on the data quality of the PMU and estimation on the angle error on site. The method comprises the following steps of: evaluating the data quality of the PMU by utilizing the difference comparison between the measured data of the RTU and the measured data of the PMU at the same physical measuring point; according to the measured data by a database of the control center in real time at the same moment, selecting the same physical measurement, carrying out difference comparison on RTU measurement and PMU measurement with normal accuracy after state estimation, evaluating the quality of the PMU measurement, and estimating the angle error of the PMU.