  At present, the theory of light diffraction only has the simple wave-optical
approach. In this paper, we study light diffraction with the approach of
relativistic quantum theory. We find that the slit length, slit width, slit
thickness and wave-length of light have affected to the diffraction intensity
and form of diffraction pattern. However, the effect of slit thickness on the
diffraction pattern can not be explained by wave-optical approach, and it can
be explained in quantum theory. We compare the theoretical results with single
and multiple slits experiment data, and find the theoretical results are
accordance with the experiment data. Otherwise, we give some theory prediction.
We think all the new prediction will be tested by the light diffraction
experiment.
