Nowadays, the studies on optical band gap and absorption spectrum of V doped ZnO have presented two distinctly different experimental results, that is, the blue shift increases and decreases when the mole fraction of impurity increases in a range from 0.0417 to 0.0625. To solve this contradiction, according to the first-principles plane-wave ultrasoft pseudopotential of the density functional theory, we set up models for a pure ZnO cell and two supercells of Zn1-xVxO (x=0.0417, 0.0625) to calculate the total density of state, partial density of state, magnetism and absorption spectrum through using the method of GGA+U. The calculation results indicate that with the doping amount increasing from 2.083 at% to 3.125 at%, the magnetic moment of doping system increases and magnetism augments, too. Moreover, the volume of doping system increases, the total energy decreases and the formation energy becomes lower, thereby making the system more stable. Meanwhile, its optical band gap becomes wider, and the absorption spectrum shifts toward low energy. The calculation results are consistent with the experimental data.