In this paper, the light double-slit diffraction with quantum theory approach is studied. Firstly, the light wave function in slits is calculated, and the diffraction wave function is obtained with Kirchhoff′s law.The diffraction intensity is proportional to the diffraction wave function da party. Futhermore, the intensity formula of light double-slit diffraction is obtained; by comparing the quantum theory calculation results and classical electromagnetic theory calculation results and the experimental date, it is found that the calculate result of quantum theory is in accordance with the experment data, but the classical electromagnetic theory calculation result with the experiment date has certain deviation. So, the quantum theory can explain the light diffraction more precisely.The proposed method can also further study the light of the single slit,many slits and grating diffraction experiment phenomena.