Aim　&　Goff　model　was　used　to　predict　the　packing　density　of　cementitious　material　including　cement,　ultra-pulverized　fly　ash　and　silica　fume.　The　mix　proportions　of　reactive　powder　concrete　(RPC)　with　different　packing　density　and　calcium-silicon　ratio　of　cementitious　material　were　designed,　and　a　strength　test　was　carried　out.　The　study　results　reveal　that　the　flexural　strength　and　compressive　strength　of　RPC　are　related　to　the　packing　density　and　calcium-silicon　ratio　of　cementitious　material.　For　the　mix　proportion　of　RPC　with　the　calcium-silicon　ratio　of　1.179,　calcium　hydroxide　reacts　with　silicon　dioxide　fully,　and　the　superfluous　ultra-pulverized　fly　ash　and　silica　fume　fill　the　voids　of　RPC.　The　packing　density　of　its　cementitious　material　is　the　largest,　and　its　strength　approaches　summit.