Plastic injection moulding processing mould steel types are general purpose, wear resistant, nitride, corrosion resistant, high mirror type, non-magnetic and pre-hardened easy cutting plastic mould steel. In addition to the feasibility analysis of the mould structure and discussion of improvement options and the design of the mould structure, the scientific selection of steel for injection moulds and heat treatment is also a very important part of the injection mould design. The wear resistance, corrosion resistance, processability and serviceability of a mould are closely related to the choice of mould steel and heat treatment, thus affecting the life of the mould application, the cost of mould manufacture and maintenance and the cycle time of mould manufacture. Although the cost of steel for moulds is only 10% to 20% of the manufacturing cost, the choice of steel and heat treatment for moulds can really determine the overall economics of an injection moulded part for the reasons mentioned above. In recent years, with the improvement of steel smelting technology, many high quality high performance steels and advanced heat treatment technologies have been formed, such as pre-hardened steels, high toughness mould steels, defect-free mould steels, corrosion resistant mould steels, mirror mould steels, easy cutting mould steels and high speed steel based steels. These steels are slightly higher in price than ordinary injection mould steels in plastic injection moulding process, but the performance is much higher than ordinary injection mould steels.