In the course of testing the insulated pipeline, because of the insulation of the insulating layer, the magnetic field generated by the traditional electromagnetic nondestructive testing technique will be badly attenuated when diffusing to the surface of pipeline. So detecting the corrosion in the insulated pipeline is a crux in nondestructive testing (NDT). Pulsed magnetic flux leakage (PMFL) technique is adopted to detect the corrosion in the insulated pipeline because it combines the advantages of richness frequency components of pulsed eddy current testing and the superiority of the magnetic flux leakage technique adapted to the inspection ferromagnetic pipeline together. Based on analyzing the principle of PMFL and by using finite element method, the distribution of magnetic field along the pipeline surface and pipeline wall, and the detection abilities of four different sensor models to the insulated layers in different thickness are studied. The result of simulation shows that the model with the core in both sides of the exciting coil has a better testing ability. Finally, the performances of this sensor are investigated by experiment; the result shows that this sensor can be used to perform quantitative detection of corrosion depth.