The invention relates to a power line leakage current analysis method, which comprises the following steps: (1) line impedance data are acquired; (2) n groups of measurement data for the head end and the tail end of the line are acquired; (3) orthogonal decomposition is carried out on each group of measurement data, and correlative components corresponding to the measurement data are acquired; (4) a 3sigma method is adopted to judge the measurement data; (5) according to a line pi-type equivalent circuit model, a data correction model based on extended state estimation is built, and m groups of measurement data after updating are acquired; (6) orthogonal decomposition is carried out on the updated measurement data, and corresponding correlative components are acquired; and (7) through least squares estimation, leakage current calculation on a single sample containing the m groups of measurement data is completed. Through the measurement data with errors at two ends of the line, cleaning, correction and orthogonal decomposition are carried out on data samples, correlative components related to hidden risk dangers are extracted, correlative leakage current components are acquired by using the least squares estimation, and the leakage current change trend is analyzed.