The electronic structure and piezoelectric properties of ZnO materials with different Mg doping contents were studied by first principles method. It is found that with the increase of Mg incorporation ratio, the ratio of ZnO lattice constant c to lattice constant a(c/a) decreases, and the band gap width increases. When the mole ratio of Mg doping is 0.3, the band gap reaches the maximum value of 1.493 eV. The calculation results of state density and differential charge density show that the reason for the increase of band gap is that the Zn-3d state in the conduction band moves towards the high-energy end. The introduction of Mg helps to improve the piezoelectric properties of ZnO materials, with the piezoelectric coefficient increasing from intrinsic 1.302 72 C/m2 to 1.355 88 C/m2. The increase of piezoelectric coefficient may be attributed to the structural distortion caused by the decrease in the value of the tetragonal factor c/a.