To　solve　the　problems　of　insufficient　identification　conditions　of　large　vehicle　barrier　in　expressway　confluence　area　under　automatic　driving　environment,　less　research　on　traffic　impact　and　more　qualitative　analysis,　a　car　following　model　with　headway　and　a　lane　changing　model　that　considers　the　safety　distance　were　established　to　form　a　cellular　automaton　model,　which　can　indicate　the　traffic　characteristics　of　the　confluence　area.　The　effects　of　macro　parameters　(flow　of　main　road　and　on-ramp　and　proportion　of　large　vehicles　on　main　road)　and　microscopic　parameters　(headway　and　length　of　barrier)　on　the　formation　of　large　vehicle　barrier　were　analyzed　quantitatively.　At　the　macro　level,　different　combinations　of　main　road　and　ramp　flow　were　obtained　when　the　large　vehicle　barrier　appears,　and　it　is　found　that　the　critical　value　of　the　formation　of　large　vehicle　barrier　is　the　proportion　of　large　vehicles　on　the　main　road　of　0.4.　The　microscopic　criterion　of　large　vehicle　barrier　is　that　three　or　more　large　vehicles　run　in　a　queue　and　the　headway　between　vehicles　is　no　more　than　1.5　s.　Additionally,　the　effect　of　large　vehicle　barrier　was　mainly　manifested　by　the　decrease　of　on-ramp　flow,　the　increase　of　on-ramp　delay　and　the　number　of　traffic　conflicts.　Results　show　that　it　can　provide　a　theoretical　basis　for　the　formulation　of　large　vehicles　management　and　control　strategy　under　automatic　driving　environment.　©　2022,　Editorial　Department　of　Journal　of　Beijing　University　of　Technology.　All　right　reserved.