Abstract: Based on the principle of magnetic flux leakage testing, COMSOL finite element software was used to study the coexistence of several common internal and external defects in pressure vessels. Using Q235 material storage tank floor plates and X60 steel material pipelines as subjects, the changes in magnetic flux leakage signals when defects existed on both the internal and external sides of the pipe wall were studied. Results showed that the axial signal was sensitive to defects with different degrees of overlap, and the left and right peak differences detected could be used for preliminary determination of the degree of overlap. Finally, verification was conducted by building a test platform. Results showed that magnetic flux leakage testing could effectively detect steel plate defects and pipeline defects with different parameters, consistent with theoretical analysis results.