The mechanical properties of BCC-series alloys subjected to various annealing temperature were investigated. The influence of severe lattice distortion effect to material’s hardness and tensile properties were analyzed. In this study, Ta, HfNbTa, HfNbTaTiZr BCC-series alloys with different degree of entropy were fabricated by vacuum arc melting and subjected to cold working. The cold worked specimens were annealed under different temperature for one hour and water quenched. With fixed annealing period, relation between microstructure and mechanical properties showed special tendency. The number of elements involved dominates the overall mechanical properties since the lattice distortion degree increases with elements number. The present research concluded this extraordinary trend and made a comparison with conventional alloys, hence helped figure out the origin of its outstanding properties through deformation behavior. With this study, it is hoped to have a better understand and an extensive utilize of refractory high entropy alloy.