Abstract: The magnetic flux leakage (MFL) of the tank plate defect is complex, and it is difficult to get enough characteristics. For this problem, different three-dimensional (3D) magnetic sensor arrays were designed to test the magnetic flux leakage of round pit defect on steel plate. The experiment results show that the linear array can distinguish primary MFL signal and secondary MFL signal and thus obtain the characteristic parameter values of circular differential in each dimension. The ring array can form the detection area on the defect so that it can get the gradient of each dimension. The cross array can resist the interference of common mode signal, reduce the disturbance of vehicle jitter and other factors. More valuable characteristic information can be acquired by the detection based on arrays.