Abstract: Considering the welded joints which are made up of power hardening mate rials,the load-displacement curves of welded joints of different mismatched strength and geometrical dimensions in plane strain were discussed by finite element method.And then,the fractureproperties of each mismatched welded joint Was analyzed using the COB-pliance-changing-rate method.In the end,the engineering estimate meth-od of the fracture facto rs and toughness of welded joints wss realized throuIgh curve simulations.