Abstract: Polyethylene terephthalate (PET) film is widely used in packaging, electronics, optical devices and other fields. However, PET itself is flammable and has a high fire hazard when applied. Adding flame retardants usually reduces the mechanical properties and light transmission characteristics of PET. How to achieve high-efficiency flame retardant of PET while maintaining the performance advantages of the material itself has become a difficult problem and challenge for PET flame retardant applications. This work uses layered self-assembly technology to alternately coat polyacrylic acid and carboxymethyl chitosan containing new two-dimensional nanomaterials M(OH)(OCH₃) (M=Co, Ni) on the PET surface, and prepare transparent and flame-retardant PET nanocomposites. The results of thermal weight loss analysis show that the amount of residual carbon in nitrogen and air of nanocomposites (PET-9BL@M) coated with 9 layers is 17.2% and 3.92% respectively, an increase of 5.1% and 3.7% respectively compared with pure PET. The conical calorigy results show that the maximum heat release rate and total heat release of PET-9BL@M are 316.1 W/g and 14.3 KJ/g respectively, which are 27.18% and 16.37% lower than pure PET, respectively, and the flame retardant is significantly improved. Condensation phase analysis shows that the high-density carbon layer generated by PET-9BL@M combustion plays a flame-retardant and protective role on the PET matrix. This work explores the flame-retardant composite coating based on the new two-dimensional nanomaterial M(OH)(OCH₃), which provides valuable references for the flame retardant application technology of PET.