According to the different working conditions and processing methods of injection mold, the basic performance requirements of injection mold steel are summarized: enough surface hardness and wear resistance. The hardness of the injection mold steel is usually below 50-60 hrc. The heat treated injection mold should have sufficient surface hardness to ensure that the injection mold has sufficient hardness. Due to the injection mold filling under high pressure and high friction and high flow process, the accuracy of injection mold is required to maintain the stability of mold shape and dimensional accuracy, and ensure the life of injection mold. The wear resistance of the injection mold depends on the chemical composition of the steel and the heat treatment hardness, thus improving the hardness of the injection mold. 2. Good processability. In addition to EMD processing, most plastic moulds also need a certain amount of machining and assembly. In order to prolong the service life of the mold, improve the cutting performance and reduce the surface roughness, the hardness of the mold must be appropriate. 3. Good polishing performance. High quality plastic products require less cavity surface roughness. For example, the surface roughness of the injection mold cavity is less than Ra0.1 ~ 0.25, while the optical surface requires Ra<0.01nm. In order to reduce the surface roughness, the cavity must be polished. The selected steel requires less impurities, uniform structure, no fiber orientation, no pitting or orange peel defects during polishing. 4. Good thermal stability. Plastic injection mold parts are more complex in shape and difficult to quench, so should choose as far as possible good thermal stability, in mold processing small linear coefficient of expansion after heat treatment, heat treatment deformation, change rate caused by small temperature difference, microstructure and mold size stability, can reduce or no longer process, can ensure Requirements for dimensional accuracy and surface roughness of injection moulds.