Unbaffled　U-shaped　mesoscale　oscillatory　flow　reactors　(meso-OFRs)　were　developed　to　prevent　solid　deposition　and　prepare　uniform　barium　sulfate　(BaSO4)　nanoparticles　with　environmental　protection　function.　The　results　showed　that　the　oscillation　significantly　reduced　granular　deposition;　the　greater　the　intensity　of　the　oscillation,　the　faster　it　reached　uniformity,　and　the　less　likely　the　granules　were　to　be　deposited.　These　results　can　be　explained　by　the　formation　of　a　larger　vortex　size,　which　can　strengthen　the　turbulent　mixing　of　fluid　in　the　reactor,　promote　the　interaction　and　forced　mixing　between　the　liquid　phase　and　solid　particles,　enhance　the　internal　shear　stress　of　the　fluid,　and　contribute　to　the　secondary　suspension　of　solid　particles　and　the　disintegration　of　particle　agglomeration.　The　prepared　BaSO4　nanoparticles　with　oscillation　were　smaller　in　size　and　lower　in　pressure　drop　than　those　produced　without　oscillation,　which　conclusively　illustrated　that　oscillation　effectively　prevented　channel　deposition　and　clogging.