The 3D UV additive production system employs a photopolymerization to build up thin layers of a part of 3D-object. We developed a one-dimensional mathematical model of the photopolymerization kinetics to elucidate the conversion of monomer and shrinkage. The photopolymerization is likely inhibited by the oxygen from air. An un-reacted layer is formed by the oxygen-inhibition reaction at the surface of photopolymerized UV resin film. Then the un-reacted layer was covered by fresh layer of UV resin and photopolymerized. There is a unique distribution of conversion of UV resin along the normal direction of the layers. The developed model enabled us to simulate the distribution of conversion in the photopolymerized UV resin layers. The conversion of functional group is related to shrinkage through the free volume reduction of the sample. Lower UV intensity is low cure shrinkage when they compared with a same height. Moreover, the curve of cure shrinkage and height of low intensity e.g., 10 mW/cm2, is more gentle than that of higher intensity. If the change of cure shrinkage is sharp, a residual stress will be stored, which will be released at the breakage at the point in the sample.