Plastic products are widely used in various fields. Due to the inherent features of high-molecular polymer, plastics are prone to show scratch under external forces, which not only influences the appearance, but also degrades the properties and the service life. Currently, hardening treatment technology has been widely developed and used and the hardening coating on the surface is a convenient method to solve this problem. Now, the domestic and foreign research progress of perhydropolysilazane (PHPS) based hardening coating is summarized and the research results for different plastics are classified. When used on PS surface, organic-inorganic coatings with high hardness were achieved due to the good compatibility between PHPS and PS derivatives. When applied to PC surface, organic-inorganic coatings with good transparency, adhesion and high hardness were obtained by controlling the PHPS/PMMA structures. The hardness of PC surface was also improved by PHPS/organosilazane derived coatings. When used on PET and PMMA surface, dense, transparent, high-adhesive and hard coatings were prepared by directly painting PHPS on the substrate surface. For application in other plastics, water vapor barrier property as well as thermal stability was enhanced. As the coating application filed expands and the protection requirement improves continuously, PHPS based coatings have great potential and wide application foreground in plastic surface hardening field in future.