Abstract: An image enhancement based on multi-scale Retinex (MSR) is proposed to solve the problem of non-uniform illumination and poor contrast of defect image in detection of fluorescence magnetic particle. The principle and implementation of the algorithm are described. Firstly, the Gaussian filter coefficients are calculated for three different scales. Then, the original image is convolved and the results are weighted and averaged. Finally, the image is truncated and pulled up to get the result. The experimental results show that compared with the conventional algorithms, the MSR not only realizes the dynamic range compression, but also improves the contrast and improves the image quality.