Abstract: Aiming at the two types of defects as affecting the quality of the 40CrMnMo seamless steel pipe, the reasons for the defects are analyzed by means of testing the alloy composition, the inclusions and the characteristics of the defect based on the manufacturing process, and accordingly corrective measures are proposed.The results show that the first type of the defect is the straight line rolling imprint which is identified via the analysis as a kind of rolling fold caused by the surface cracks of the rolling tool;the second defect is the crack of the pipe body which is recognized as quenching crack caused by excessive quenching-cooling speed.Finally the above mentioned quality problem of the pipe is fixed by means of improving the quality of the rolling tool and optimizing the quenching process.