Dense sandstone formation is a common difficult-to-drill section in oil and gas drilling, and its difficult-to-drill nature lies in the complex composition of rock minerals and dense cementation, coupled with the multiscale interaction of in situ temperature and pressure coupling in the endowment environment, which makes its mechanical characteristics more complex and difficult to be effectively characterized by existing experimental means. For this reason, starting from the fine-scale thermal expansion characteristics of the skeleton/cemented minerals, combined with the polycrystalline discrete element method, a non-homogeneous fine-scale mechanical modeling method considering the temperature effect was established and used to reveal its triaxial compression characteristics. The results show these as follows. Unlike the thermal expansion and contraction characteristics of skeleton minerals, the spacing of clay mineral grain surfaces shows irreversible thermal expansion with increasing temperature, which is the fundamental reason for the mechanical properties of locally strengthened dense sandstones; the thermal expansion of clay minerals increases the contact strength of intergranularity, and the localized densification makes the intergranularity more difficult to be damaged during triaxial compression, and the percentage of intragranular tensile cracks rises with the temperature; the compressive strength and elastic modulus of clay minerals increase with the temperature at room temperature~200 ℃, compressive strength and modulus of elasticity increases with temperature, the increase of peripheral pressure makes the elastic modulus growth trend from “lower convex” to “upper convex”. 30 MPa, room temperature to 200 ℃, the compressive strength increased by 21.6%. At 200 ℃, the compressive strength increased by 26.6% from 0.1 to 30 MPa. The results provide a theoretical tool for prediction of pre-drilling mechanics for drilling wells in deep dense sandstones.