One of the advantages of the phasor measurement unit (PMU) is to provide synchronous phase angle data. However, due to factors such as abnormal time synchronization, device failures and other factors, some of the measured PMU phase angle data are abnormal, which could affect the PMU application. This paper proposes a method for correcting the time?varying deviation of PMU phase angle difference (PAD) at both ends of the line based on line reactive power loss. Firstly, based on the measured value and estimated value of the line reactive power loss, a single?time PAD deviation estimation model is constructed; Secondly, aiming at the problem that the single?time estimation model is greatly affected by noise, based on the relationship between the voltage PAD and the line parameter, the time?varying deviation estimation model by single?snapshot data is transformed into a constant line parameter estimation model by multi?snapshots data; after estimating the line parameters through the golden section search algorithm, the PAD deviation can be calculated by the PMU amplitude and power data, the estimation and correction of the time?varying PAD deviation at multiple times are realized. The test results of simulated and measured PMU data from a province show that the method could accurately estimate the PAD deviation and has strong anti?noise ability. Compared with the existing methods, this method only needs data under single power flow condition to realize the estimation and correction, and is suitable for the correction of different types of time?varying deviation.