Abstract: Three-dimensional SEM image reconstruction of hematite flocculates is an important method to observe the internal structure of flocculates and plays an important role in studying the flocculation effect of flocculates.The flocculates are processed by freeze vacuum drying method, and SEM images of hematite flocculates are obtained by scanning electron microscopy(SEM).MATLAB software is used to preprocess the SEM image of hematite flocculate obtained in the experiment to reduce the influence of irrelevant factors on the image and lay a foundation for subsequent three-dimensional reconstruction.By extracting three-dimensional data and setting three-dimensional display effect, three-dimensional reconstruction of the SEM image of hematite flocculate is realized.The results show that the reconstructed three-dimensional image has a better stereoscopic display effect, and the undulation degree of particles and pores can be observed more intuitively.In the image, the raised part is the particle, while the concave part is the pore.The particle is concentrated in the center of the image, and the pore is distributed in the middle of the particle and the edge of the image.The reconstructed three-dimensional image provides an important basis for the subsequent study of three-dimensional porosity and three-dimensional fractal dimension of flocs.