The　displacement　discontinuity　method　(DDM)　has　been　commonly　utilized　to　investigate　the　wave　propagation　in　the　jointed　rock　mass,　in　which　the　joint　thickness　is　assumed　to　be　infinitely　thin.　However,　naturally　filled　joints　are　usually　thick.　To　investigate　the　wave　propagation　through　the　thickly　joint　and　evaluate　the　applicability　of　DDM　in　studying　stress　waves　through　the　thickly　joint,　a　study　of　stress　waves　across　the　filled　joints　with　thickness　was　conducted.　The　wave　transmissions　through　rock　mass　with　different　joint　thicknesses　and　wave　impedance　ratios　of　the　rock　and　joint　were　analyzed.　The　effects　of　the　joint　thickness　and　wave　impedance　ratio　on　wave　transmission　coefficient　were　discussed.　Finally,　the　accuracy　of　DDM　prediction　was　validated.　The　results　show　that　the　transmission　coefficient　decreases　as　joint　thickness　and　wave　impedance　ratio　increase.　It　is　noted　that　the　prediction　accuracy　of　DDM　is　affected　not　only　affected　by　joint　thickness,　but　also　highly　affected　by　wave　impedance　ratio　in　front　of　and　behind　the　joint.　The　prediction　accuracy　of　DDM　decreases　as　the　joint　thickness　and　wave　impedance　ratio　increases.　DDM　studies　the　wave　attenuation　with　high　accuracy　when　the　joint　thickness　and　wave　impedance　ratio　are　small.