Study　on　acoustic　testing　method　for　mechanical　properties　of　thin　layer　materials.　Based　on　Legendre　orthogonal　polynomial　method,　linear　independent　equations　are　constructed　and　the　reflection/transmission　coefficient　of　acoustic　waves　at　the　interfaces　is　calculated　using　liquid/solid　boundary　conditions　and　wave　control　equations.　The　method　analyzes　the　influence　of　the　cut-off　order　on　the　solution　result,　and　finds　the　critical　value　of　the　order　under　different　frequency　and　thickness　products,　then　calculate　the　reflection/transmission　coefficient　based　on　the　cut-off　order.　The　calculation　results　obtained　by　the　Legendre　orthogonal　polynomial　method　are　compared　with　those　obtained　by　the　transfer　matrix　method,　and　the　accuracy　of　the　theoretical　model　is　verified.　Ultrasonic　waves＇　oblique　incidence　into　a　thin-layer　material　forms　a　Lamb　wave.　The　dispersion　characteristics　at　the　steady　state　are　intrinsically　linked　to　the　reflection　features.　According　to　Snell＇s　law,　the　three-dimensional　surface　of　the　frequency-velocity-reflection　coefficients　is　calculated　using　the　Legendre　orthogonal　polynomial　method.　This　result　is　compared　with　the　dispersion　curves　simulated　by　Disperse.　It　is　proved　that　the　solving　result　is　consistent　with　the　Lamb　wave　dispersion　characteristics.　The　influence　of　attenuation　on　the　experimental　results　during　the　propagation　of　the　acoustic　wave　is　reduced　by　collecting　the　reference　signal　which　is　the　directly　obtained　wave　without　a　sample.　A　reflection　and　transmission　experimental　system　was　built　to　measure　the　frequency　spectrum　of　reflection　and　transmission　coefficients　at　different　incident　angles.　The　experimental　results　are　compared　with　the　theoretical　results,　and　the　accuracy　of　the　results　obtained　by　the　theory　is　verified.　A　solving　methodology　without　root-finding　algorithm　for　acoustic　reflection/transmission　coefficients　is　realized.　This　method　provides　a　theoretical　basis　and　experimental　guidance　for　the　non-destructive　testing　of　the　mechanical　properties　of　thin-layer　materials.　©　2020,　Editorial　Board　of　JBUAA.　All　right　reserved.