Abstract: Addressing the fact that nonconformance of impact energy and yield strength are found with heavy wall drill collar pipe bodies in batch as being heat treated by a certain domestic drill collar processing factory,analyses concerning the chemical composition,mechanical property,metallographic structure and hardness of the pipes are conducted.As a result,it is identified that both the rather slow water-cooling speed as uesd and circumferential water cooling inhomogeneity as occurred during the water quenching process lead to the obvious strength fluctuation and low impact energy of the pipe. Accordingly based on the production practice,it is proposed to take such actions as increasing Mn and Cr contents in the steel to improve the hardenability,enhancing the water cooling speed,and periodically checking the quench tank water temperature and the spray nozzle status so as to further stabilize the product performance.