A microstructural model of heavy tungsten alloys is offered. On the basis of this model and several assumptions, the effects of tungsten content on micro-mechanical behavior and macro-mechanical properties of the heavy tungsten alloys under tensile deformation are analyzed using computer numerical simulation. The tungsten content is assumed to be within the range of 80 wt% to 95wt %. The results show that the yield strength of the heavy tungsten alloys increases with the tungsten content, while both the elastic deformation and the elongation decrease. The variation of tensile strength with tungsten content is not monotonic. For tungsten contents<85 wt%, the tensile strength increases with the increase of the tungsten content, while the tensile strength decreases strongly for tungsten contents >85 wt %. At a tungsten content of 85 wt %, the tensile strength is a maximum. This behavior is explained in terms of the stress distribution between the tungsten grains and the matrix phase. In the alloys with low tungsten content (<90wt % ), the high stress concentrates in tungsten grains. As the tungsten content increases, the stress in matrix phase decreases slightly. In the case of high tungsten content, however, the maximum stresses in tungsten grains and matrix phase are the same, and higher tungsten content results in higher stress in matrix phase.