In　the　traditional　discontinuous　deformation　analysis　(DDA)　method,　the　implicit　time　integration　scheme　is　used　to　integrate　equations　of　motion　for　modeling　the　mechanical　behavior　of　a　highly　discrete　rock　block　system.　This　requires　that　global　equations　be　constantly　solved.　Hence,　the　computational　efficiency　of　the　traditional　DDA　method　will　decrease,　especially　when　large-scale　discontinuous　problems　are　involved.　Based　on　the　explicit　time　integration　scheme,　an　explicit　version　of　the　DDA　(EDDA)　method　is　proposed　to　improve　computational　efficiency　of　the　traditional　DDA　method.　Since　a　lumped　mass　matrix　is　used,　there　is　no　need　to　assemble　global　mass　and　stiffness　matrices.　More　importantly,　solving　large-scale　simultaneous　algebraic　equations　can　be　avoided.　The　open-close　iteration,　which　can　assure　the　correct　arrangement　of　constraints,　is　kept　in　the　EDDA　method.　In　addition,　the　simplex　integration　method,　which　is　capable　of　conducting　exact　integration　over　an　arbitrarily　shaped　block,　is　employed.　Two　numerical　examples,　including　a　sliding　problem　with　an　analytical　solution　and　an　underground　cavern,　are　solved.　The　numerical　results　indicate　the　accuracy　and　robustness　of　the　proposed　EDDA　method.