Single-particle　trapping　mechanisms　into　microcavities　are　still　puzzling　for　size-based　particle/cell　sorting　in　microfluidics.　Aiming　to　verify　the　prediction　of　particle-wall　collision　trapping　mechanism,　we　explore　the　effects　of　the　microcavity　trailing　wall　on　the　single-particle　trapping　behaviors　for　various　microcavity　aspect　ratios　(lambda　=　0.5-5)　and　inlet　Reynolds　numbers　(Re　=　5-400),　uncovering　three　new　trapping　phenomena,　namely,　contact　trapping,　collision　trapping,　and　rapid　trapping.　We　characterize　the　particle　velocity　variation　during　the　trapping　process.　We　also　investigate　the　separatrix　topology　(streamlines　between　the　microvortex　and　microchannel　flow)　and　map　the　different　particle　trapping　phenomena.　The　particle　trapping　results　from　the　combined　effects　of　the　microcavity　trailing　wall,　the　separatrix　topology,　and　the　particle　dynamics.　The　results　provide　new　insight　into　the　fundamental　understanding　of　particle　trapping　mechanisms　and　could　guide　the　applications　of　microcavity-based　microfluidics.　Published　under　license　by　AIP　Publishing