Abstract: In order to meet the needs of train brake disc defect detection, electromagnetic tomography (EMT) was used in the system. The position, shape and size of the defect can be shown after the images reconstructed with the detected information based on the EMT. According to the structure characteristics of train brake discs, a flat-type sensor coil array was designed. Electromagnetic simulation software was adopted to simulate the brake disc models with different defects, four algorithms were used for defect imaging reconstruction, and the qualities of images were compared by different evaluation indexes. The simulation results verified the feasibility of the electromagnetic tomography technology used in train brake disc defect detection. An experimental system was built based on the experimental results to obtain data and reconstruct images. The experimental results show that the electromagnetic tomography technology has a good application prospect in the detection of brake disc defects.