Abstract: Natural soils generally have cemented material between particles, which can be referred to as cemented soils, and the strength behavior and its mechanism of weakly cemented soils at common mean stresses are dependent on the mean stress. In addition, the strength of cemented soils under low mean stress, which exhibits significant nonlinearity and is difficult to be measured, is essential in engineering problems such as slope tensile strength cut-off and stability of shallow excavation. For this reason, the discrete element method was adopted to generate numerical specimens of weakly cemented sand by installing a bond contact model between particles, which were subjected to isotropic tensile/compression, constant p triaxial tests (including p<0 and p>0) and constant p true triaxial tests. The results show that the stress-strain relationships of cemented sand in triaxial tests can be classified as three cases: under the low confining pressure (p < σ_y), the strength envelope exceeds the critical state line q = Mp, and therefore the stress-strain relationship shows strain softening, which microscopically corresponds to a quick decrease in the stress contribution of bond contacts and a slow growth in stress contribution of frictional contacts; under the medium confining pressure (σ_y < p < (p_c−p_t)), the stress-strain relationship is higher than that of the remolded sand at low axial strain, and strain hardening is observed, and microscopically corresponds to a decrease in the stress contribution of bond contacts and a faster growth in stress contribution of frictional contacts; under the high confining pressure (p>(p_c−p_t)), the stress-strain relationship is close to that of the corresponding remolded sand, with a considerable decrease in the stress contribution of bond contacts and a much faster growth in stress contribution of frictional contacts. In all three cases, cemented and remolded sands have roughly the same critical strength. The strength envelope in the p-q space of the weakly cemented sand can be described using the extended elliptical surface at p < σ_y and incorporates the critical state strength line at p > σ_y; in the π plane, both the critical and peak strength envelope can be described using the Lade-Duncan criterion.