Abstract: Internal erosion is one of the main causes of seepage damage in natural sediments or geotechnical structures. In the seepage process, particle shape is an important factor affecting the development of erosion in soil. A transparent soil seepage test device was designed independently. Based on the spherical harmonic algorithm and 3D printing technology, samples with 3D printed transparent particle with specified shape characteristics were prepared. Seepage internal erosion tests of discontinuous graded soils with different particle shapes were carried out to explore the influence of particle shape on the development of internal erosion in discontinuous graded soils. The mesoscopic mechanism of the erosion development process in soils with different particle shapes was further revealed by combining transparent soil technology. The test results show that particle shape is an important factor in determining the characteristics of internal erosion. The sample composed of elongated particles with a small aspect ratio AR have a higher fine particle erosion ratio and a faster erosion speed than the sample composed of spherical particles, and the growth rate of permeability coefficient during internal erosion is also greater; the skeleton formed by angular particles with a larger spherical harmonic factor d_2-8 (particle shape parameter) has better stability, and its fine particle erosion ratio, erosion speed, and growth rate of permeability coefficient during seepage are smaller. In addition, the internal mesoscopic map of transparent soil reveals that the differences in pore throat structure between the coarse particle skeletons is the fundamental reason for the different development of internal erosion under different particle shapes.