The time-frequency distribution(TFD)fits to process the Lamb Wave since it is typical non-stationary signal.It is well know that HHT is a signal processing method with perfect time frequency characteristic.Active Lamb wave has been increasingly wide utilized in plates structural health monitoring.Its wave packets are research target key,because wave packets were superimposed by damage scattering signal if plate was damaged.But The IMF from Wave packets EMD cant directly extract instantaneous character before and after damage.The difference between the same state signals IMF is so big that the instantaneous character can not explain the influence of damage scattering signal to wave packets.This paper studied the reason abnormal EMD of active Lamb wave packets.Two methods to correct the EMDs abnormal result were suggested based on the research.In the experiment,the method improved the effect of Lamb wave packets EMD.