Simulation　of　interaction　problems　between　rock　structure　and　soil　is　a　challengeable　subject.　It　involves　a　coupled　system　that　considers　the　behaviors　of　both　rock　structure　and　soil,　together　with　interaction　between　them.　Discontinuous　deformation　analysis　(DDA)　is　suitable　for　analyzing　a　blocky　system,　such　as　rock　or　flexible　structure.　On　the　other　hand,　smoothed　particle　hydrodynamics　(SPH)　is　appropriate　for　studying　flow　-like　behavior　of　soil　after　implementing　a　proper　constitutive　model.　A　coupling　scheme　that　bridges　DDA　and　SPH　can　take　advantages　of　both　methods.　Therefore,　a　numerical　method　for　such　interaction　problems　using　DDA　and　SPH　is　developed,　in　which　a　Drucker-Prager　elasto-plastic　soil　constitutive　model　is　incorporated.　In　the　developed　method,　the　interaction　between　SPH　particle　and　DDA　block　is　idealized　through　a　new　spring-dashpot　contact　model　with　the　Mohr-Coulomb　failure　criterion　used.　Several　numerical　examples　are　studied,　and　satisfactory　agreements　between　the　simulation　results　and　the　experimental　data　or　other　available　simu-lated　results　are　obtained,　suggesting　the　correctness　of　the　developed　method.　Further,　the　developed　method　is　applied　to　study　influence　of　backfill　on　a　masonry　arch　bridge.　Conclusively,　this　coupled　DDA-SPH　method　provides　a　potential　numerical　approach　for　studying　interaction　problems　between　rock　structure　and　soil.