Abstract: It is generally accepted that landfilled municipal solid waste（MSW）exhibits heterogeneity and anisotropy because of the diverse composition and the layered placement, causing that the distribution of pores prefers to be horizontal. In the landfill, the preferential flow is obvious, and the anisotropy is significantly affected by the overburden pressure. According to the changes of pore shape, pore size distribution and pore alignment under compression, a saturated permeability model is derived based on the Poiseuille equation, which mainly relates to the dominant flow and its anisotropy. The pore distribution changes of fresh MSW are revealed. Under the overburden pressure of 0~200 kPa, with the collapse of larger pores, the pore average size and drainable porosity decrease according to the negative exponent, and the pore alignment tends to be horizontal. When calculated by the new model, the drainable porosity can well simulate the variation of permeability. The preferential flow is dominated by the large pores. Under the overburden pressure of 0~600 kPa, the saturated horizontal permeability of fresh MSW is in the range of 10^-2~10^-5 cm/s. The formula for the permeability anisotropy is given. The calculated permeability anisotropy of fresh MSW increases for the correction to the direction of pore alignment. Under the overburden pressure of 0~600 kPa, the value is in the range of 1~10.