Abstract: For small diameter pipe circumferential crack detection problem, do the finite element simulation. Utilize an magnetic conductor coil axial eddy current test to detect small diameter tube circumferential crack defect.The simulation shows magnetic field distributions eddy current distribution and the receiving coil voltage,when pipeline in the case of defects and defect-free state. From the simulation results can be observed that the magnetic field and eddy currents distribution of circumferential cracks at the ends changed significantly, and generating a magnetic field along the normal to the wall. The induced voltage reaches the maximum value when the detection coil just above the ends of the crack. The actual testing results are in accordance with the simulation results,showing that magnetic conductor coil axial eddy current technique for small diameter pipe circumferential defect detection effect is remarkable.