The surface quality and properties of gypsum mold were very high in low pressure casting. Based on years of experience in low-pressure casting aluminum alloy pattern blocks and the establishment of shrinkage database, the influence of gypsum surface coating on shrinkage of pattern blocks was analyzed. It mainly includes performance research of strong cold coating, spraying technique, coating thickness, spraying time, drying time, etc. When applied to practical production, the shrinkage porosity rate of the pattern block is greatly reduced, the shrinkage porosity defects of the cast aluminum pattern block is improved, and the production cost is reduced.