Particle/cell　separation　from　a　mixture　using　a　hydrodynamic　vortex　has　been　attracting　much　interest　for　the　isolation　of　circulating　tumor　cells　in　basic　biological　studies　and　clinical　applications.　However,　some　issues　regarding　the　particle　recirculating　orbits　within　the　vortex　in　microcavities　remain　unclear.　In　this　work,　using　micro-particle　image　velocimetry　and　a　high-speed　microscopy　system,　we　quantitatively　investigate　the　effects　of　inlet　Reynolds　numbers　(Re)　on　the　microcavity　flow　characteristics　and　particle　recirculating　behavior.　The　results　show　that　due　to　the　evolution　of　microcavity　flow　patterns　(Re　=　15-313),　the　particle　orbit　topology　expands　gradually,　developing　from　a　single　small　orbit　(Re　=　39-79)　to　a　single　semicircular　orbit　(98-117),　then　to　alternating　double　orbits　(Re　=　136-215),　and　at　last　to　a　single　large　orbit　(Re　=　254-352).　The　alternating　double　orbits　are　observed　for　the　first　time.　The　particle　orbit　periods　and　topologies　(lengths　and　area)　have　also　been　characterized.　Moreover,　the　variations　of　the　recirculating　particle　velocity　are　also　quantitatively　measured.　The　results　deepen　the　fundamental　understanding　of　particle　recirculating　behavior　and　could　provide　useful　guidance　for　vortex-based　microfluidics.