Abstract: The application of wavelet-transformation to alarming in loose parts monitoring system(LPMS) was studied. On the base of analyzing the main factor to the erroralarming in LPMS,the alarming theory in view of wavelet's RMS was established by choosing minor scale of relative noise as alarming datum point,and the base noise which affect alarm was checked effectively.Moreover RMS threshold and time width RMS threshold wavelet alarming algorithm were adopted,all make the alarm more dependable.