The　ultrasonic　non-destructive　evaluation　of　elastic　constants　based　on　acoustic　microscopy　utilizes　a　point-　or　line-focus　transducer　to　perform　the　immersion　defocusing　measurement　towards　the　specimen,　so　that　the　acoustic　properties　can　be　obtained　and　used　to　inverse　the　mechanical　properties.　In　practical　engineering　applications,　problems　like　the　dimensions　of　workpiece　are　too　large　or　the　workpiece　can　not　be　immersed　in　water　are　frequently　encountered,　resulting　in　the　inapplicability　of　defocusing　measurements.　In　order　to　solve　this　kind　of　problems,　a　new　type　colloidal　coupling　medium　was　developed.　This　colloidal　coupling　medium　possesses　many　advantages　such　as　easy　to　prepare,　low　cost,　easy　to　clean　off,　environment　friendly.　The　formulations　are　optimized　through　many　different　proportion　experiments,　in　order　that　the　acoustic　characteristics　(density,　sound　velocity,　acoustic　impedance)　can　match　the　water.　Then,　this　coupling　medium　was　used　in　the　ultrasonic　non-destructive　evaluation　of　elastic　constants　of　aluminum,　steel　and　titanium　specimens.　The　experimental　results　were　consistent　with　the　ones　using　water　as　coupling　fluid,　and　show　great　agreements　with　the　theoretical　values　and　the　results　by　conventional　tensile　test.　A　practical　measurement　on　elastic　constants　of　large　scale　aluminum　plate　was　also　carried　out,　and　the　results　coincides　with　the　theoretical　ones.　Thus,　this　study　shows　that　the　evaluation　results　by　this　new　type　colloidal　acoustic　coupling　medium　can　meet　the　demands　of　defocusing　measurements　using　focusing　ultrasonic　transducers.　It　offers　an　effective　technical　method　to　the　engineering　application　of　ultrasonic　non-destructive　evaluation　of　elastic　constants　based　on　acoustic　microscopy.　©　2016,　The　Editorial　Board　of　Journal　of　Basic　Science　and　Engineering.　All　right　reserved.