To　solve　the　problem　of　micro-crack　direction　detection　in　metal　structures,　a　method　of　measuring　micro-crack　direction　based　on　harmonic　nonlinearity　was　developed.　The　influence　of　the　crack　direction　on　the　ultrasonic　scattering　field　was　analyzed　by　numerical　simulations　of　the　nonlinear　interaction　between　the　micro-crack　and　the　ultrasonic　wave.　The　simulation　results　show　that　the　increase　of　the　second　harmonic　and　the　third　harmonic　propagation　direction　of　the　reflected　longitudinal　wave　is　about　twice　that　of　the　crack　direction,　and　the　propagation　direction　of　the　harmonic　component　of　the　transmitted　longitudinal　wave　is　almost　unchanged.　The　above　results　were　applied　to　the　measurement　of　arbitrary　micro-crack　direction.　The　results　show　that　the　method　can　measure　the　micro-crack　direction　and　the　error　is　small.　©　2018,　Editorial　Department　of　Journal　of　Beijing　University　of　Technology.　All　right　reserved.