A relative wave crest detecting algorithm base on all the tenses is proposed aiming at how to detect the number of medium layer on multilayer penetration. The algorithm mainly uses time information as a basis for the layer number recognition, then utilizes the polarity of the difference between the wave peak apex and the data points before and after it to preliminary identify the number of the wave peak, then bases on pulse width and fengfeng interval information for number of peaks for further confirmation in order to improve the correction of recognition the number of medium layer. The algorithm is feasible and correct in data processing through simulation and shooting range test. The algorithm provides a new design thought for the penetration layer recognition, does not rely solely on peak, makes full use of time and amplitude information of the signal comparing with the existing absolute threshold comparison method.