A variety of metal ions were used to modify melamine polyphosphate (MPP),creating metal ion-modified MPP (referred to as J-MPP), which was then compounded with aluminum diethylphosphinate (ADP) to enhance the flame retardancy of PA6/GF composite materials. The investigation focused on the impact of different metal ions on the flame retardant and mechanical properties of the PA6/GF flame retardant system. The results demonstrated that the PA6/GF/J-MPP composites exhibited superior flame retardant performance compared to the PA6/GF/MPP system. Notably, the PA6/GF composite containing aluminum ion-modified MPP (Al-MPP) achieved a UL-94 V-0 rating in vertical burning tests, with a limiting oxygen index (LOI) reaching 31.7%. Additionally, the total heat release (THR) of the PA6/GF/Al-MPP composite was reduced to 139.1 MJ/m2, and the char residue increased to 41.5%, indicating that Al-MPP significantly improves the condensed phase flame retardant effect of the PA6/GF composite material. The introduction of metal ion-modified MPP also contributed to the enhancement of the composite material’s mechanical properties. Compared to the PA6/GF/MPP system, the PA6/GF/J-MPP composites showed improvements in mechanical performance, particularly the PA6/GF/Mg-MPP, whose notched impact strength increased to 8.5 kJ/m2, an increase of 14.9%.