Improving　the　rock-breaking　efficiency　of　hard　rock　formation　has　always　been　of　concern　in　drilling.　Compound　impact　drilling　technology　is　a　new　method　to　achieve　efficient　crushing　of　hard　rock　by　exerting　axial　and　torsional　impacts　on　the　drilling　bit.　In　this　study,　to　investigate　the　dynamic　rock　breaking　process　and　mechanism　under　compound　impact,　a　numerical　model　was　developed　based　on　cohesive　elements.　Dynamic　impact　tests　on　sandstone　were　conducted　to　verify　the　effectiveness　of　the　method.　Then,　the　dynamic　rock-breaking　process　under　compound　impact　was　simulated　using　the　proposed　model.　Finally,　the　effects　of　impact　parameters　and　cyclic　loading　on　the　rock-breaking　performance　were　systematically　studied.　The　results　indicate　that　the　stereoscopic　crushing　effect　of　rock　can　be　achieved　under　compound　impact.　The　amount　of　broken　rock　increases　with　the　increase　in　the　impact　load　amplitude　and　impact　loading　times,　whereas　both　the　impact　angle　and　duration　have　an　optimal　range.　When　the　impact　angle　is　30　degrees,　the　impact　duration　is　2.5　ms,　the　amount　of　broken　rock　is　maximum.　A　novel　compound　impact　drilling　tool　was　designed　based　on　the　analysis　of　the　rock-breaking　mechanism,　the　laboratory　and　field　tests　were　carried　out　and　the　parameters　were　optimized.　(C)　2021　The　Authors.　Published　by　Elsevier　Ltd.