Nondestructive detection of small fatigue cracks is a critical and challenging task in evaluating the properties of material. This article proposes a novel L-shaped ferrite magnetic open sensing structure of the eddy current pulsed thermography system for fatigue crack inspection on metallic materials with anomalistic geometry. The theoretical derivation model of the proposed structure is developed to generate a guided distribution of electromagnetic field for enhancing the weak thermal signal detection. The proposed detection model provides a region of interest that has relatively uniform magnetic field. This significantly enhances the detectability and thermal contrast of omnidirectional microfatigue cracks. In addition, the detection is completely in the open view of the infrared camera, and the configuration has advantages of dramatically increasing portability and efficiency for detecting complex workpiece. Experiments on natural cracks in several samples have been conducted to validate the reliability and efficiency of the proposed system.