Based　on　tangent　modulus　theory　and　Derived　Proportional　Law　(DPL),　elastic-plastic　fracture　is　analyzed.　Through　a　comparison　of　parameters　between　tangent　modulus　factor　and　fracture　toughness,　a　new　method　for　calculating　elastic-plastic　critical　stress　fracture　is　established.　The　Experimental　datum　identifies　that　this　method　has　the　equivalent　accuracy　with　COD　method　and　has　wider　range　of　applications.　The　results　also　show　that　from　the　stress-strain　relationship　and　improved　strain　relationship,　a　J-integral　expression　can　be　obtained.　It　provides　a　new　way　to　calculate　the　value　of　the　J-integral.　©,　2014,　The　Editorial　Board　of　Ship　Building　of　China.　All　right　reserved.