Reaction Injection Molding (RIM) is a new process for rapid prototyping, it injects the mixed PU materials into the rapid mold under the normal temperature and low pressure environment, to form the parts according to the polymerization、cross linking、solidification and other chemical or physical reaction of the PU materials. Its advantages are high efficiency、short production period、simple operation and low cost. It is suitable for trial production of the big cover products with small amount manufacturing、simple structure and even thickness.