Abstract: By the application of the principle of linear transition between electricity and light of LED,optical fiber voltage transformer overcomes the shortcomings of traditional electromagnetic transformer,and realizes the insulating of electricity and magnetism between high and low voltage sides,the monitoring for power quality.In the paper in view of the instability of the frequency of power net, the interpolation algorithm and data processing software were applied to correct the frequency and frequency error,amplitude and phase of all harmonic waves.And the transformer can carried out the analysis and calculation of harmonic,phase discrimination,power factor,active and reactive power together with PC.