Metallographic analysis on surface peeling and cracking defects for tensile samples of 12 mm thick hot rolled high strength steel plate by light and electron microscope.The results showed that temperature of upper and lower billet surface when heated is not synchronous,lower surface decarburization was serious,and made the rolling steel form a layer of even all the decarburization layer.Surface decarburization layer was tilted and crazed with tensile stress.The industrial analysis showed that the holding time of billet when heated is the major factor whether or not controlling lower surface decarburization,if holding time was more than 190 minutes in the furnace,would aggravate slab of the lower surface oxidation and decarburization.Through the determination of fracture toughness for finished product hot-rolled steel plate,found defect depth formed by decarburization layer was much smaller than the critical value of the unstable propagation of material,thus determine the reliability of the product,and give measures to improve the surface quality.