In a southern landfill, 6samples weighing about 5kg were collected at the depth of 5~30m. The samples were sieved and sorted to study the variation of the particle composition with the depth. Meanwhile, the samples under different loads were stained and sectioned to analyze the influence of overburden pressure on the internal structure of MSW. The results showed that the fine particles (0D, i.e., particle size <2cm) were the most content in the MSW samples and its proportion exceeded 50%. The proportion of 2D particles was the highest in coarse particles, and the plastic was the most content in the 2D particles. As the load increased, the content of fine particles increased, while the large pores and preferential flow channels decreased. The overburden pressure mainly reduced the internal pore space of MSW, and then decreased its hydraulic conductivity. 2D particles could be directionally arranged under loading, which led to the tortuosity of seepage path and the anisotropy of hydraulic conductivity. The directional arrangement of 2D particles was the key factor resulting in the seepage anisotropy of MSW, and the plastic was the most important factor.