The characteristics of precision injection molding are: the size of injection parts requires high precision and small tolerance. To achieve the requirements of precision injection molding must achieve the weight conditions are :(1) the material of the mold is good, rigid enough, the dimensional accuracy of the cavity and the positioning accuracy between the templates should be high, the surface roughness should be low. (2) to use precision injection molding machine. (3) to use precision molding process. (4) to choose materials suitable for precision injection molding process. The commonly used precision injection molding materials are as follows: POM\POM=CF(carbon fiber), PNM=GF(glass fiber), PA\FRPA66 (enhanced PA) \PC, etc. In the process of precision injection molding, the important method to ensure the precision size of injection parts is to control the shrinkage of injection parts, including: thermal shrinkage, deformation shrinkage, orientation shrinkage, compression shrinkage and elastic recovery of injection parts. The characteristics of ordinary injection molding are: the dimensional accuracy requirements of injection molding parts are not high, generally can be assembled as the standard, the appearance requirements of injection molding parts are relatively high, when necessary, may use the second processing (such as oil injection) to improve the appearance of defects. Ordinary injection molding does not need to use special precision injection molding machine, also do not need special specified materials, commonly used thermoplastics can be used to produce. So the common injection molding process is widely used in the modern plastic industry.