CrMoNbTiVx (x=0, 0.2, 0.4, 0.6, 0.8) refractory high entropy alloys with different addition of vanadium were prepared, and the phase constitution, microstructure characteristics and oxidation properties at elevated temperature were investigated. Results show that the as-cast CrMoNbTiVx alloys with different addition of vanadium exhibit single body-centered cubic (BCC) crystal and form dendrite structure. After oxidation at 800 ℃ for 20 h and 100 h, weight gains of CrMoNbTi alloy are 0.25 mg/cm2 and 0.50 mg/cm2, respectively, while weight gains of CrMoNbTiV0.8 alloy are 1.49 mg/cm2 and 3.36 mg/cm2, respectively. Weight gains of CrMoNbTiVx alloys are decreased with decreasing of vanadium, and the surface of oxidation layer gets smoother with decreasing of vanadium. Height differences of CrMoNbTiV0.8 and CrMoNbTi after oxidation for 100h are 24.80 μm and 3.37 μm, respectively. The oxidation products of alloys with different addition of vanadium are different, and the V2Nb6O19 needle shape oxidation products can obviously reduce the oxidation properties of CrMoNbTiVx alloys. Reducing the addition of vanadium can promote formation of compact oxidation products of TiO2, CrVNbO6 and Ti4Cr3Nb3O2, and therefore improve oxidation properties of CrMoNbTiVx alloys. V2Nb6O19, CrVNbO6 and V2O5 in oxidation layer of CrMoNbTiVx alloys are reduced with decreasing of vanadium. The oxidation layer of CrMoNbTi without addition of vanadium is consisted of compact TiO2 and Ti4Cr3Nb3O2, and therefore the oxidation resistance is significantly improved.