The　dynamic　response　characteristic　of　rockfall　impact　cushion　is　the　key　basis　of　rock-shed　design.　As　an　important　feature　of　cushion　particle　size　distribution，gradation　determines　the　distribution　of　particle　size　and　affects　the　dynamic　process　of　rockfall　impact　cushion.　To　study　the　influence　of　particle　gradation　on　the　dynamic　response　of　rockfall　impact　cushion，the　numerical　simulation　of　the　dynamic　response　of　cushion　with　different　gradations　is　carried　out　by　using　a　discrete　element-finite　difference　coupling　algorithm.　Under　the　condition　that　the　average　particle　size　is　equal，through　the　analysis　of　impact　force，central　compressive　stress，and　impact　depth　of　falling　rock，the　dynamic　response　mechanism　of　rockfall　impact　particle　cushion　is　revealed.　The　results　show　that：　the　stability　of　the　force　chain　between　particles　determines　the　dynamic　response　characteristics　of　the　cushion　after　impact.　The　friction　between　particles　is　the　main　way　of　energy　consumption，accounting　for　70%–80%　of　the　energy　consumption.　For　single-peak　grading，the　smaller　the　particle　size　of　the　single　peak　is，the　longer　the　force　chain　length　is，and　the　weaker　the　stability　is.　When　the　peak　particle　size　dt　=　75　mm，the　peak　impact　force　is　1.9　times　that　of　dt　=　25　mm，and　the　peak　compressive　stress　is　3.6　times.　For　bimodal　gradation，the　closer　the　distance　between　the　two　peaks　is，the　less　the　number　of　constraints　around　the　particles　is，and　the　worse　the　stability　of　the　force　chain　is.　When　the　heterogeneity　coefficient　He　=　0.65，the　peak　impact　force　is　40%　larger　than　that　when　He　=　0.33，and　the　peak　compressive　stress　is　30%　larger.　The　uniformity　of　particle　distribution　determines　the　response　characteristics　of　the　cushion　after　impact.　©　2023　Academia　Sinica.　All　rights　reserved.