The equilibrium geometries, vibrational frequencies of VOxH2O (x= 15) and interactions between H2O with VOx(x= 15) are studied by using the density functional theory B3LYP/DZP method. The results show that ground states for VOxH2O (x= 15) belong to C1 point group symmetry,their electronic state is 2A, and in ground state of VOxH2O (x= 1, 4, 5) water molecule H2O is dissociated; H2O molecule is absorbed easily in VOx(x= 15) and VOxH2O(x= 15) are formed; In VOxH2O(x=15), chemical activations of VOxH2O (x= 1, 4, 5) are lower than those of VOxH2O (x= 2, 3); the sequence of interaction strength between H2O and VOx(x= 15) is VO4H2O VO5H2O VOH2O VO3H2O VO2H2O; there is possibility that OH segment and H atom are dissociated easily from VOH2O and VO5H2O, respectively by visible light exposure. Criterion that H2O molecule is dissociated in VOxH2O(x= 15) is obtained by analyzing frequency spectrum.