Based　on　the　propagation　characteristics　of　microwave　and　the　microwave　sensitivity　to　the　interface,　the　phase　difference　at　the　interface　of　thermal　barrier　coating(TBC)　and　waveguide　probe　was　used　to　characterize　the　long　crack　on　the　metal　substrate　surface　under　TBC　using　computer　simulation　technology-microwave　studio　(CST-MWS).　The　influences　of　top　coating　thickness　and　crack　direction　were　studied.　Besides,　microwave　evaluation　of　cracks　with　different　width　and　the　crack　length　direction　parrallel　to　the　long　brim　of　the　rectangular　waveguide　probe　were　studied　when　the　thickness　of　TBC　is　400　μm.　The　results　show　that　the　top　coating　thickness　affects　the　sensitive　frequency,　and　that　the　carck　direction　influences　the　evaluation　sensitive,　and　the　evaluation　sensitive　is　the　minimum　when　the　angle　between　the　rack　length　direction　and　the　long　brim　of　the　rectangular　waveguide　probe　is　50°-55°.　It　is　also　observed　that　the　crack　can　not　be　detected　when　the　crack　width　is　less　than　8　μm,　and　the　effect　of　detection　is　not　obvious　when　the　crack　width　is　10-30　μm,　and　the　wider　the　cracks,　the　greater　the　phase　difference　of　the　reflection　coefficient　when　crack　width　is　in　the　range　of　30　μm-1　mm.　Therefore,　it　is　feasible　to　evaluate　the　crack　on　the　metal　substrate　surface　using　microwave　non-destruction　evaluation.