In practical production, the heavy forgings of the largest diameter 1225 mm larger than its length 905 mm are unqualified for supersonic inspection. By means of acid-eroding, scanning electron microscopy and energy spectrum analysis on defects, it is shown that the defects are originated from inclusions made up of Al2O3, Fe2O3 and a little CaO. In order to improve forging quality, the controlling mechanism of defects is analyzed, and forging process of two times upsetting and stretching process is researched to eliminate the cracks originated from inclusions. The result shows that the inclusions in forgings can be controlled and the inner cracks recovered effectively by two times upsetting and stretching process. All of the forgings meet the supersonic standard which indicates that this process is better fit for heavy forgings with largest diameter larger than its length.