Abstract: The inspection of oil and gas pipelines is mainly based on the method of magnetic flux leakage (MFL) detecting.In order to optimize the size of magnetic path structure in a magnetic flux leakage (MFL) inspection tool,Kirchhoff's first law and second law were adopted.Using finite element method (FEM) to optimize the magnetic circuit of the magnetic flux leakage inspection tool and combining it with previous results,it significantly reduced the volume of magnetic circuit part and the weight of the magnetic flux leakage inspection tools.