800　MPa　ultrafine　grain　steel　is　a　new　generation　steel　with　excellent　mechanical　properties.　But　thermal　effect　of　welding　may　lead　to　grain　growth　and　local　softening　in　heat-affected　zone.　Evaluation　of　anti-fracture　performance　for　welded　plate　was　carried　out　using　numerical　analysis　approach.　Using　MARC　commercial　software,　tensile　plate　models　of　both　all　base　steel　and　welded　joint　with　various　center　through　crack　sizes　were　computed　by　three-dimensional　finite　element　method,　and　the　tensile　process　was　simulated　at　the　same　time.　The　welding　method　used　was　a　PC-GMAW　process　with　mixture　gases　shielding.　Central　crack　for　the　welded　plate　was　located　in　the　fusion　zone　between　welding　seam　and　heat-affected　zone.　The　base　steel　plate　for　making　comparison　was　the　same　crack　size,　crack　location,　finite　element　meshes　and　boundary　condition　as　the　welded　plate.　The　effect　of　weld　mechanical　heterogeneity　on　the　stress-strain　fields　of　the　welded　plate　was　analyzed.　On　the　basis　of　the　full　yield　criterion,　CTOD　value　of　welded　joints　was　compared.　The　results　indicate　that　the　CTOD　values　of　welded　joint　are　lower　than　those　of　all　base　plate　of　identical　crack　length.　Thus,　the　welded　plate　exhibits　priority　of　anti-fracture　performance　over　all　base　plate.　The　local　softening　in　the　welded　joint　does　not　cause　unfavorable　influence　on　structural-load-carrying　capacity.