The　failure　location　identification　of　granular　materials　can　be　solved　by　capturing　the　deformation　localization.　Considering　the　relative　translation　and　rotation　among　particles,　a　new　concept　named　the　relative　particle　motion　(RPM)　is　proposed　to　describe　the　deformation　localization　of　the　granular　materials.　An　approach　is　developed　to　realize　the　selection　of　particles　that　are　used　to　calculate　RPM.　The　number　of　particles　involved　in　RPM　calculation　is　controlled　by　two　key　parameters,　i.e.,　grid　spacing　(U)　and　domain　radius　(R).　Combining　the　proposed　concept　and　the　selection　approach　of　particles,　the　method　that　can　capture　the　region　of　the　deformation　localization　in　the　granular　material　is　established　and　implemented　in　PFC2D.The　simulation　of　a　uniaxial　compression　test　is　conducted　to　analyze　the　effect　of　parameters　U　and　R　on　the　calculation　results　of　the　RPM　field,　and　a　reasonable　range　of　U　and　R　is　given.　Three　typical　conditions,　including　the　biaxial　compression,　trapdoor,　and　particle　flow　tests,　are　taken　as　examples　to　validate　the　proposed　method　under　different　loading　conditions.　Regions　of　the　deformation　localization　characterized　by　RPM　have　a　good　agreement　with　the　shear　band　presented　in　the　published　literature.