The behaviors of helium in vanadium including stability, diffusion, and its interaction with vacancy as well as its effects on the ideal tensile strength was investigated by a first-principles method. The activation energy barrier of helium was calculated to be 0.09 eV, which is consistent with the experimental result. The results indicated that the vacancy can lead to a directed helium segregation into the vacancy to form a helium cluster since the vacancy provides a “lower atomic and electron density region”as a large driving force for helium binding. It is easy for a mono-vacancy to trap helium and form a HenV complex. The first-principles computational tensile test demonstrates that helium obviously decreased the tensile strength of vanadium.