Abstract: In view of the petroleum and petrochemical cylindrical vessels characteristics, this article applied the magnetic flux leakage testing to such vessels. The application of ANSYS software simulation for magnetic flux leakage testing of cylindrical vessels was analyzed together with those influencing factors on defects magnetic flux leakage signals, such as the defect size, vessel wall thickness, inside and outside wall defect etc. On the basis of this, experimental studies were carried on cylindrical vessels, which confirmed part of the analysis results and verified the accuracy of finite element analysis.