We reported the hydrogen (H) interacting with the vacancy-oxygen (V-O) pairs complexes and its effect on H accumulation behavior in bcc vanadium in comparison with alone vacancies using first-principles calculations. The H interaction with interstitial O atom is weak repulsion and all interstitial sites near O atom are unstable for H. The alone mono-, di- and trivacancy defects can trap 6, 8-11 and 13 H atoms, while one V-O pair, two V-O pairs, and three V-O pairs complexes trap approximately same about 4-6 H atoms, respectively. The formation of O-vacancy pairs weakens the binding energy of the VmHn clusters, the number of trapped H atoms is drastically reduced to form nearly sized H clusters. We presented the stable configurations of various VmHn and VmOmHn complexes (with m = 1-3 and n = 1-15), the most stable configurations are the V1H2/V2H2/V3H2 clusters in alone vacancies, while there are the V1O1H/V2O2H/V3O3H clusters in the V-O complexes. In presence of alloying Ti near (V-O) pair, one Ti(V-O) pair complex still trap four H atoms, but the H binding strength has some changes. These results demonstrated that the existence of the multi-V-O complexes significantly reduce the growth and swelling of the H clusters. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.