The oblique crack is a major form of damage to the rail tread surface. When it reaches a certain depth, these cracks will rapidly expand and cause transverse fractures in the rail head. Therefore, the detection of oblique cracks on rail treads is of great significance for railway safety. Based on the characteristics of rail tread detection, a rail tread oblique crack detection system has been developed and tested using the alternating current field measurement (ACFM) technique. The ACFM detection model is established using the finite element software COMSOL. It analyzes the response relationships between the induced electromagnetic field and the oblique cracks, as well as explores the influences of different scanning paths on the distortion of characteristic signals. In consideration of the rail tread's characteristics, the detection probe, scanning frame, and detector are designed, and the detection software is written to form a complete rail tread oblique crack detection system capable of detecting rail tread cracks of various lengths and depths. Simulation and experimental results demonstrate that the distortion of the characteristic signal at the center position of the oblique crack is the smallest, while the characteristic signal at the end position is the largest. The detection system can effectively detect oblique cracks as deep as 1 mm on the rail tread increases, the distortion of the crack center characteristic signal increases, and as the length of the crack increases, the distortion of the characteristic signal first increases and then decreases.