Abstract: The aim of this research is to analyze the influence of shrinkage behavior on the deformation of forming parts in mask projection stereolithography. A mask projection stereolithography machine based on DLP( digital light procession) technology was designed, and the shrinkage of photosensitive resin during light-cured process was analyzed. The shrinkage behavior of resin in different exposure situations, free-surface and constrain-surface, and also in secondary curing process was studied. The result shows that in free-surface, the shrinkage of B5B type resin is proportional to the exposure time, eventually it stabilizes at around 4%. When it is in constrain-surface, the overflowed light curing effect leads to shrinkage which decreases with exposure time increased, and the shrinkage generated in the secondary curing process accounts for 40% ~50% of total.