The flame retardance of glass fiber reinforced polymers is an important worldwide challenge due to the wick effect caused by glass fiber. In this paper, an interfacial flame resistance mode was proposed in order to solve the problem in an efficient and economic manner. Unlike the conventional bulk flame resistance mode based on a high loading of flame retardants distributed evenly throughout the entire composite matrix, the interfacial flame resistance mode concentrates only a very low content of flame retardants located in the glass fiber–polymer interfacial regions, where the wicking action occurs, grafted on the glass fiber surface. According to this new mode, glass fiber reinforced and flame retarded polyamide 6 was prepared and evaluated. At the combustion temperature, the interaction between the polymer (polyamide 6) and the grafted flame retardant quickly produced inert and rough interfacial chars replacing the original smooth and high-energy surface of the glass fiber. The interfacial char layer could effectively block the adsorption, wetting, spread and flow of the polymer melt on the glass fiber surface, therefore, greatly weakening both the thermodynamic and dynamic processes that induce the wicking action. In addition, the formation of organic side chains on the glass fiber surface by the graft reaction also contributed to an improvement in the interfacial compatibility, favoring enhanced mechanical properties of the composites. The interfacial flame resistance mode provided a novel means for preparing advanced flame retardant glass fiber reinforced polymers.