Abstract: The causes of drawing cleavage brittle fracture of large gauge high carbon steel 82B wire rod are analyzed by carrying out metallographic structure inspection and analysis.They are found out as the result of Mn,Cr central segregation causing formation of martensite in the centre of the wire rod,and the center martensite fracture becomes one of the sources of crack in the process of drawing because of the difference of deformation rate between the central part and the other area.There are some defects of scar and scratches near the fracture surface.It is manifested,through deeper analyzing,the main cause of drawing cleavage brittle fracture is the combined action of central martensite and surface defect.The incidence rate of cleavage brittle fracture defect has been reduced effectively through optimizing the content of Mn and Cr and improving the technics of steelmaking,rolling and drawing.