Abstract: A microstructure model of tungsten heavy alloys has been developed. On the basis of the model, the micro-mechanical behavior of tungsten heavy alloys under tensile deformation has been analyzed by computer numerical simulation with finite element method (FEM).The results show that the maximum stress is in the tensile direction and the maximum Mises stress is in tungsten grains, and there is a compressive stress in them, which is perpendicular to the tensile direction. The maximum shear stress and the first plastic flow in tungsten heavy alloys take place in matrix under tensile deformation. As the tensile deformation increases, the stress concentrates onto tungsten grains.