<p>Polyethylene (PE), a ubiquitous thermoplastic polymer, is extensively utilized in packaging, construction, electronics, and automotive industries owing to its exceptional chemical resistance, processability, and cost-effectiveness. However, its intrinsic flammability, characterized by a low limiting oxygen index (LOI) of 17.4% and rapid melt-dripping behavior during combustion, poses severe fire hazards, hindering its application in aerospace, electrical insulation, public infrastructure, and some areas with high fire prevention requirements. To address this limitation, the development of flame-retardant PE composites has emerged as a pivotal research frontier. This paper first introduces the combustion process and reaction mechanisms of PE materials. It then reviews the application of flame retardants in PE and their effects on the flame retardancy of these materials. The advantages, limitations, and synergistic effects of these additives are discussed, alongside future directions for sustainable flame-retardant technologies. The flame retardants discussed include phosphorus-based flame retardants, inorganic flame retardants, expanding flame retardants, and biomass-based flame retardants.</p>