Harmonics analysis is used in on-line tanδ measurement on-line.When there is a frequency fluctuation in network

under the condition of the signal with harmonics

it is difficult to achieve synchronous sampling

and accuracy will be influenced by leakage error.In this paper

the reasons of the leakage error under asynchronous sampling in the frequency domain are analyzed

and the weighted harmonics analysis algorithm based on the definition of tan δ can improve the precision of measuring effectively.Simulation results have proved the validity and feasibility of the method.