Swirl　atomizer　inner　core　is　the　most　important　swirling　component　of　the　pressure　swirling　atomizer,　the　geometric　topology　of　the　swirl　atomizer　inner　core　directly　affects　the　spray　characteristics　of　pressure　swirling　atomizer.　The　current　smooth　acceleration　section　of　the　swirl　atomizer　inner　core　has　lower　flow　efficiency.　In　order　to　reduce　the　energy　loss,　the　swirl　atomizer　core　accelerating　section　with　ladder　type　has　been　designed　to　make　spray　medium　pre-swirl　and　enhance　the　swirl　strength　in　this　paper,　the　lower　part　rotates　15°　relative　to　the　upper　part,　and　the　direction　of　the　rotation　is　the　same　as　the　direction　of　the　swirling　slots　of　the　atomizer.　Spray　flow　rate,　spray　Sauter　mean　diameter(SMD),　spray　cone　angle　and　droplet　velocity　were　experimentally　investigated　by　making　use　of　particle　dynamics　analysis　system(PDA)　and　charge　coupled　device　experimental　system(CCD)　before　and　after　the　structure　improvement　of　the　acceleration　section,　and　the　axial　and　radial　distributions　of　SMD　and　droplet　velocity　were　also　analyzed.　Under　the　pressure　ranges　from　0.08　MPa　to　0.46　MPa,　the　ladder　type　acceleration　section　has　the　better　pre-swirl　effect.　The　flow　characteristics　of　the　atomizer　were　increased　by　48%　to　51.8%;　the　axial　and　radial　velocity　of　the　spray　were　increased　by　31.4%　to　32.8%　and　1.6%　to　16.8%,　respectively.　The　spray　cone　angle　was　reduced　by　4.21°　to　6.57°,　and　the　SMD　at　downstream　of　the　spray　was　decreased　by　9.2%　under　higher　pressure　conditions.　Compared　with　the　smooth　accelerating　section,　the　application　of　ladder　type　accelerating　section　is　beneficial　to　improve　the　quality　of　atomization.　©　2018,　Editorial　Office　of　Chinese　Journal　of　Theoretical　and　Applied　Mechanics.　All　right　reserved.