This　paper　combined　digital　image　processing　(DIP)　and　discrete　element　method　(DEM)　to　investigate　the　relationship　between　the　particle　characteristics　of　manufactured　sand　and　the　flow　ability　of　mortar,　and　clarified　the　key　characteristics　parameters　of　particle　shape　influencing　the　flow　ability　of　mortar.　A　method　for　batch　calculation　of　shape　characteristic　parameters　(elongation　ne,　angularity　index　na　and　fullness　ratio　nf)　of　aggregates　based　on　DIP　was　proposed.　The　fluidity　tests　and　corresponding　simulations　of　mortar　at　different　water-cement　ratios　were　carried　out　respectively,　and　the　results　showed　that　the　errors　of　simulated　fluidity　(fm)　were　around　7%.　The　simulation　results　demonstrated　that　the　fm　decreased　with　increasing　content　of　large-size　aggregates　in　the　mortar.　The　augment　of　both　ne　and　na　reduced　the　flowability　of　mortar.　The　magnitude　of　rolling/sliding　friction　coefficients　of　aggregates　are　the　important　parameters　that　determine　the　flowability　of　mortar.