This paper presents the thermal-mechanical coupled model of polycrystalline aggregates based on plastic slip theory inside crystals and on the interfaces of crystals. It involves the mechanics and heat conduction behaviors caused by both force loads and temperature changing in the polycrystalline aggregates. At first, the constitutive relationship inside single crystal, and the moment equations and energy equations are derived by means of rate-dependent plastic deformation theory and the formulas of elastic-plastic tangent modulus depended on temperature. And those on crystal interfaces are also given. Based on the ABAQUS software , the subroutines to calculate the tension, torsion and bending strength of polycrystalline copper are coded. The numerical simulation results show that breakages occurred more easily on the interfaces than other areas of the polycrystalline aggregates, especially for bending loading and torsion loading, and that’s consistent with results by molecular dynamics but their computing cost are less and less than MD simulation.