The principle of mathematical morphology filtering and the structure of the morphology filter are introduced.A new mathematical morphology filter based on morphological open and closed operators and their cascade combination is presented to analyze the partial discharge（PD） signals from the typical defect models of oil-paper insulation.With the filter

real PD signals with heavy disturbance are well smoothed in analysis.Compared with the existing filters in practical applications

the present mathematical morphology filter is more effective in de-noising

and implements high frequency signal filtering without time delay and phase shift

which indicates that this method is suitable for analyzing pulsed PD signals.