Abstract: The causes of disqualified mechanical properties of HRB500 hot rolled ribbed bar were analyzed by optical microscopy, scanning electron microscopy, energy disperse spectroscopy and tensile testing. For the causes of mechanical properties disqualification, some improved process measures were given, and the microstructure and mechanical properties of the ribbed bar after improving also were analyzed. The results show that the important reasons for disqualification tensile strength of the ribbed bar are the serious banded structure, manganese sulfide and silicate inclusions and low concentration of N element. After the improvement measures, such as increasing the N content, adopting slag washing process in steel making, prolonging the time of blowing argon and controlling the speed in continuous casting process, are adopted, the banded structure in the HRB500 hot rolled ribbed bars dramatically reduce and the inclusion is not found, the mechanical properties of the ribbed bar can satisfy the requirements of Chinese standard.