A digital exposure apparatus for a color enlarging photo printer is disclosed, in which an exposure unit comprising a Liquid Crystal on Silicon, a polarization splitting prism, a condenser lens, a light source, and a digital enlarging objecting lens, wherein the optical axis of the Liquid Crystal on Silicon, the polarization splitting prism and the digital enlarging objective lens coincides with the optical axis of the printing lamp, the filter and the mixed light barrel. The whole structure of this apparatus is simplified and the light intensity of existing digital exposure apparatus is increased. The technology is advanced so that the digital exposure apparatus will be more productive.