The application of electromagnetic tomography (EMT) in the detection of the distribution of magnetic catalysts in biodiesel preparation is studied. Based on a sensor array with 8-coil TMR coil structure, the simulation experiment is designed, and the imaging results of catalysts with different particle sizes are compared. The research shows that the coil structure is suitable for the distribution detection of magnetic catalysts. In order to improve the shortcomings of the traditional imaging algorithm, the application of the matching pursuit algorithm (CoSaMP) in image reconstruction is studied, and compared with the traditional Tikhonov algorithm and Landweber algorithm, the results show that the CoSaMP algorithm has better edge processing ability and faster imaging speed. Compared with the other two algorithms, the image error is reduced by 30. 4% on average, and the imaging speed is increased by 46%, which effectively improves the quality and speed of reconstructed image.