The　water-immersion　non-eollinear　shear　wave　mixing　method　was　explored　for　fatigue　crack　detection.　Using　the　developed　water-immersion　non-collinear　shear　wave　mixing　detection　system　and　the　signal　processing　method　of　polarity　reversal,　the　experiments　of　fatigue　crack　inspection　were　carried　out,　and　the　influences　of　the　two　exciting　waves＇　interaction　angle　and　frequency　ratio　on　wave　mixing　effect　were　studied.　Then,　the　two-dimensional　automatic　scanning　inspection　was　conducted　on　the　sample　blocks　with　fatigue　crack.　It　is　shown　that　the　polarity　reversal　method　can　be　used　for　wave　mixing　effect　extraction.　The　optimal　interaction　angle　and　frequency　ratio　in　the　case　of　fatigue　crack　deviate　from　the　resonance　conditions　of　the　classical　nonlinear　ultrasonic　wave　mixing　theory.　The　fatigue　cracks　in　the　steel　structure　can　be　detected,　located　and　quantified　by　using　the　two-dimensional　scanning　of　non-collinear　shear　wave　mixing.　The　work　makes　a　beneficial　exploration　for　the　engineering　application　of　the　technique　of　nonlinear　ultrasonic　wave　mixing.　©　2023　Chinese　Vibration　Engineering　Society.　All　rights　reserved.