Abstract: Standard defects and magnetic flux leakage inspecting probes were classified in this paper, and the probes were studied, focusing on the signal characters and their merits and drawbacks of different types, such as the spot and linear, based on their applications on the hole defects, the linear and the volume ones, respectively. The design principle with specimen-objective of magnetic flux leakage inspecting probes was provided in the end. Spot-probe was suitable for inspection of the defects depth, linear-probe to defects cross-section, spot-array or spot-linear combination type to defects length information. As to the notch oblique to the magnetization direction, spot-array was the only applicable type.