Mo specimens with different initial relative density were prepared by a vacuum sintering technique. The effects of the initial relative density on the flow stress of the sintered Mo powder were studied by room temperature quasi-static uniaxial compression tests at a MTS810 universal material testing machine. The mathematic model of the flow stress and the calculation model of the elasto-plastic parameters for the sintered Mo powder were established. Based on the yield criterion and plastic constitutive equation for compressible dense materials, the yield function and the elasto-plastic constitutive model of the sintered Mo powder during compression deformation was determined.