Abstract: Mechanical behavior of municipal solid waste (MSW) is important to geoenvironmental engineering; and it is necessary to understand it properly. Laboratory direct shear tests are conducted on MSW with 3 short fill ages, namely 1 d, 4 d and 7 d. Three different densities are taken into accounted in each fill age. Experimental data show that MSW’s shear failure still satisfies the Mohr-Coulomb criterion. As to bigger density, shear strength of MSW increases within 1-7 d fill age. When density becomes smaller, its shear strength increases within 1-4 d fill age but decreases within 4-7 d fill age. With fill-age developing, friction angle of MSW increase monotonously, but cohesion force of it first increases and then decreases. On the other hand, shortcomings of traditional shear stress-displacement model are analyzed; and one composite tangent- exponential model is proposed. The proposed model has good mathematical behaviors and more applicability than traditional models. Experimental data show that it can well describe MSW’s stress-displacement curve with correlation coefficient bigger than 0.99. This research results are helpful for design and numerical simulation of corresponding MSW landfill