Finite element method (FEM) was used to investigate the plastic deformation and densification for porous molybdenum in isothermal canned forging. Separate simulations were performed using different sheath materials: 45 steel, 304 stainless steel and GH4169. The simulations demonstrated that the distributions of strain, density and average stress strongly depended on the sheath materials. The distributions of density and strain presented the shape of “U”. The density and strain, increases with increasing of strength for sheath materials at same levels of deformation. The homogeneity of strain and density was best in billet encapsulated with the 304 stainless steel when the deformation extent exceeded 40%. The average stress decreases linearly with increasing of distance from center except for small area near the edges. Among the three materials, the 304 stainless steel was the most suitable materials as sheath during isothermal canned forging of porous molybdenum.