A virtual harmonic system based on the development platform of LabVIEW is developed. The basic design idea of this system is virtual instrument(VI)．The system is suitble to add the harmonic signal collecting from actual electrified wire netting，and also load the platform simulating harmonic signal coming into being．And the on-line harmonic monitoring is carried out through this system to reveal the state of its basic wave and harmonic waves． During the analysis of harmonics，FFT algorithm with high accuracy is used to improve accuracy of harmonics analysis．This system has advantages of better analyzed effection and low cost，and can be extended easily．