Phase　locking　of　a　laser　diode　(LD)　array　in　an　external　cavity　based　on　Talbot　cavity　was　studied　theoretically　and　experimentally.　On　the　foundation　of　near　field　distributions　of　supermodes,　far　field　distributions　of　in-phase　mode　and　out-of-phase　mode　were　obtained　in　the　focal　plane　by　using　diffraction　lens　outside　of　the　cavity.　According　to　the　distributions　of　the　in-phase　mode　and　the　out-of-phase　mode　in　the　Talbot　cavity,　it　can　be　seen　that　ZT/2　cavity　(the　round　trip)　is　preferable　for　phase　locking　of　LD　arrays.　But　ZT/2　cavity　only　allows　out-of-phase　mode　oscillating,　and　the　far　field　distribution　is　double　lobes,　which　is　not　suitable　in　most　cases.　If　the　external　mirror　is　tilted　by　an　angle　of　α,　the　diffraction　images　of　in-phase　mode　exactly　coincide　with　the　apertures,　while　out-of-phase　mode　is　imaged　exactly　in　between　the　apertures,　resulting　in　high　loss.　Distributions　of　in-phase　mode　and　out-of-phase　mode　are　obtained　in　the　experiment　for　both　cases,　and　the　divergence　angle　of　far　field　single　lobe　is　1.96　mrad.