Abstract: Wavelet packet decomposition( WPD) can not only detect integral harmonics  of non-stationary signal,but also detect non-integral harmonics of it;and because  wavelet transformation singular is very sensitive to signal of the strange point,it can be used to follow the conduction interference signal in switches power supply.In virtual instrument( VI) LabVIEW 6.i software workbench,algorithm design based on wavelet packet decomposition  is developed,combined with virtual instrument (VI) program,which realizes real-time detection system of the conduction interference signal in switches power supply.The system presented here has the measurement functions  following：signal-noise separation,power spectrum of conduction interference,original vibration wave with noise and noise wave etc.The result shows that that method is feasible and effective.

Key words: wavelet packet decomposition, virtual instrument, conduction interference, power spectrum, real-time detection