In order to increase the accuracy of the online monitoring of shunt reactor, an online identification method for false overcurrent alarm of 500 kV shunt reactor based on the logical regression and Principal Component Analysis (PCA) method is proposed. Firstly, the influences of measurement error of the transformers including the PT in the bus connected to shunt reactor and the CT in the reactor branch on the conditional probability of overcurrent alarms are analyzed. Then the central point and the uncertain domain of the logistic regression function are defined as the two-dimension key indicators for the detection of false alarms, and PCA method is used to generate the one-dimension comprehensive index. Finally, the validity of overcurrent alarm is judged by comparing the comprehensive index of the detection day with that under normal conditions. The proposed method only uses the RMS of voltage in the bus connected to shunt reactor and the overcurrent alarm information obtained from monitoring system, so no additional measurement equipment is needed. The effectiveness of the method is verified by case study of a practical 500 kV high voltage shunt reactor. This work is supported by Key Research and Development Program of Sichuan Department of Science and Technology (No. 2017GZ0163) and Science and Technology Program of State Grid Corporation of China (Technology Research of Supercomputer-based Power System Operation Mode Calculation Platform Support).