In　order　to　solve　the　obstacle　avoidance　problem　in　complex　unstructured　environment,　inspired　by　the　optical　flow　navigation　strategies　of　insects,　an　algorithm　of　visual　obstacle　avoidance　for　autonomous　mobile　robot　was　developed　in　this　paper,　which　is　suitable　for　complex　unstructured　environment.　In　order　to　reduce　the　influence　of　illumination　changes　and　noise,　improve　the　calculation　accuracy　and　robustness　of　the　optical　flow　algorithm,　the　gradient　constancy　assumption　was　introduced　and　the　local　was　weighted.　And　the　flow　divergence　was　used　to　calculate　the　relative　depth　time-to-contact　(TTC).　Then　an　obstacle　map　was　constructed　based　on　the　TTC.　When　robots　were　at　risk　of　collision　with　the　obstacles,　the　heading　direction　decision　algorithm　was　designed　for　robot　to　choose　the　optimal　direction.　Simulation　and　physical　experiments　were　done　in　this　paper.　Experimental　results　show　that　the　presented　method　can　guarantee　a　mobile　robot　wander　without　collision　in　unknown　complex　unstructured　environments.　©　2017,　Editorial　Department　of　Journal　of　Beijing　University　of　Technology.　All　right　reserved.