The　flow　fields　generated　by　the　acoustic　behavior　of　microbubbles　can　significantly　increase　cell　permeability.　This　facilitates　the　cellular　uptake　of　external　molecules　in　a　process　known　as　ultrasound-mediated　drug　delivery.　To　promote　its　clinical　translation,　this　study　investigated　the　relationships　among　the　ultrasound　parameters,　acoustic　behavior　of　microbubbles,　flow　fields,　and　delivery　results.　SonoVue　microbubbles　were　activated　by　1　MHz　pulsed　ultrasound　with　100　Hz　pulse　repetition　frequency,　1:5　duty　cycle,　and　0.20/0.35/0.70　MPa　peak　rarefactional　pressure.　Micro-particle　image　velocimetry　was　used　to　detect　the　microbubble　behavior　and　the　resulting　flow　fields.　Then　HeLa　human　cervical　cancer　cells　were　treated　with　the　same　conditions　for　2,　4,　10,　30,　and　60　s,　respectively.　Fluorescein　isothiocyanate　and　propidium　iodide　were　used　to　quantitate　the　rates　of　sonoporated　cells　with　a　flow　cytometer.　The　results　indicate　that　(1)　microbubbles　exhibited　different　behavior　in　ultrasound　fields　of　different　peak　rarefactional　pressures.　At　peak　rarefactional　pressures　of　0.20　and　0.35　MPa,　the　dispersed　microbubbles　clumped　together　into　clusters,　and　the　clusters　showed　no　apparent　movement.　At　a　peak　rarefactional　pressure　of　0.70　MPa,　the　microbubbles　were　partially　broken,　and　the　remainders　underwent　clustering　and　coalescence　to　form　bubble　clusters　that　exhibited　translational　oscillation.　(2)　The　flow　fields　were　unsteady　before　the　unification　of　the　microbubbles.　After　that,　the　flow　fields　showed　a　clear　pattern.　(3)The　delivery　efficiency　improved　with　the　shear　stress　of　the　flow　fields　increased.　Before　the　formation　of　the　microbubble/bubble　cluster,　the　maximum　shear　stresses　of　the　0.20,　0.35,　and　0.70　MPa　groups　were　56.0,　87.5　and　406.4　mPa,　respectively,　and　the　rates　of　the　reversibly　sonoporated　cells　were　2.4%　+/-　0.4%,　5.5%　+/-　1.3%,　and　16.6%　+/-　0.2%.　After　the　cluster　formation,　the　maximum　shear　stresses　of　the　three　groups　were　9.1,　8.7,　and　71.7　mPa,　respectively.　The　former　two　could　not　mediate　sonoporation,　whereas　the　last　one　could.　These　findings　demonstrate　the　critical　role　of　flow　fields　in　ultrasound-mediated　drug　delivery　and　contribute　to　its　clinical　applications.