A　YLS-6000　fiber　laser　was　used　to　weld　high　strength　steel　E36　with　a　thickness　of　6　mm.　The　main　composition　(wt.-%)　of　high　strength　steel　E36　is　0.15C,　1.40Mn,　0.31Si,　0.04Al,　and　0.08Ni.　The　morphology,　tensile　strength　and　microhardness　of　butt　joints　were　studied　by　using　scanning　electron　microscopy　(SEM),　a　tensile　tester　and　a　microhardness　tester.　The　results　showed　that　butt　joints　of　high　strength　steel　E36　consist　of　a　weld　seam　(WS),　a　heat　affected　zone　(HAZ)　and　a　base　metal　(BM).　The　microstructure　of　the　WS　is　mainly　composed　of　lath　martensite,　and　the　microstructure　of　the　HAZ　is　mainly　composed　of　martensite,　bainite　and　ferrite.　The　hardness　of　the　WS　increases　with　an　increase　in　laser　power,　and　the　maximum　hardness　of　the　butt　joint　appears　in　the　transition　zone　between　WS　and　HAZ.　When　laser　power　reaches　3500　W,　the　maximum　microhardness　is　450　HV.　The　laser　power　has　little　effect　on　the　tensile　strength　of　the　butt　joint.　All　tensile　specimens　were　broken　at　the　base　material.　There　is　many　dimples　on　the　fracture,　and　the　butt　joint　displays　a　ductile　fracture.