Abstract: The layered media normal mode theory has been well established in the middle of the last century,but few attentions have been paid to the particle velocity field.The combined descriptions of the pressure field and particle velocity field in Pekeris waveguide,especially the vertical acoustic intensity flux are proposed.The result of the study shows that either the horizontal or vertical acoustic intensity flux has both active and reactive component because of the interference between the normal modes.When an acoustic vector sensor is placed appropriately,the reactive component of the vertical acoustic intensity flux in low frequency acoustic field can be used to tell the source's specified depth, although it can't transport energy.Then the reactive component of the vertical acoustic intensity flux is of importance for vector signal processing.The pressure and particle velocity cross spectra signal processing algorithm is proposed to distinguish the targets.