Air　side　heat　transfer　and　fluid　flow　characteristics　of　four-row　slotted　fin　surfaces　with　arc-type　and　X-type　strip　arrangement　in　pressurized　air　cooler　were　studied　by　visualization　experiments.　Experiments　were　carried　out　with　PIV　(particle　image　velocimetry)　system　and　infrared　thermo　tracer　to　visualize　the　flow　field　and　the　temperature　distribution　of　two　slotted　fin　surfaces.　The　experiment　results　showed　that　the　fluctuation　intensity　and　pressure　drop　of　the　X-type　slotted　fin　surface　were　higher　than　those　of　the　arc-type　slotted　fin　surface.　However,　the　heat　transfer　performance　and　field　synergy　property　of　the　X-type　slotted　fin　surface　were　superior　to　those　of　the　arc-type　fin　surface.　A　new　definition　of　fluctuation　intensity　was　proposed　to　indicate　the　magnitude　of　flow　disturbance　enforced　by　the　configuration　and　arrangement　of　slotted　fin　surface.　The　higher　the　fluctuation　intensity,　the　larger　the　velocity　gradient　and　the　vorticity　magnitude.　The　visualization　experiment　results　provide　a　reliable　experimental　support　for　later　numerical　simulation　and　optimization　design　for　new　fin　structures.