Magnetic exchange interaction for the μ-hydroxo bridged vanadium (IV) dimers is investigated based on calculations of density functional theory combined with the broken-symmetry approach. It is found that there is an exponential correlation between the V-O (hydroxo)-V angle, the V-O (hydroxo) distance and the exchange coupling constants J. Meanwhile, the calculated results reveal that the deprotonation of the bridging hydroxo ligand causes a sharp increase of the exchange coupling interaction, but the magnetic coupling constant J is insensitive to the deprotonation of the bridging aquo ligand. Moreover, simplifying each 1,2-bridging squarate ligand with two OCH2 groups almost does not influence magnetic exchange behavior between the two vanadium (IV) ions, and the principle of the shortest superex-change pathway is available for the multiplicity of the bridging ligand in the μ-hydroxo bridged vanadium (IV) di-mers.