Abstract: Polymeric materials are inherently flammable and prone to oxidation. Traditional intumescent flame retardants exhibit drawbacks, including significant moisture absorption, limited flame-retardant efficacy, and suboptimal matrix compatibility. To address these challenges, a trinity intumescent flame retardant (PTA-PA) was synthesized, integrating the principles of gas-phase and condensed-phase flame retardation. This study examined the influence of varying PTA-PA concentrations on the flame resistance and mechanical properties of polyurea (PUA). It entailed analyzing combustion and pyrolysis byproducts to elucidate the mechanism of flame retardance provided by these novel agents. Additionally, the study correlated the introduction of PTA-PA with enhancements in thermal stability, flame retardance, and overall fire safety of the composites. The findings indicate that the PUA composite with a 20.0wt% loading of PTA-PA (PUA-4) exhibits increased thermal stability, evidenced by a residual carbon content of 21.9% at 800℃. Notably, the vertical burn rating of PUA-4 improved from V-2 to V-0, the limiting oxygen index (LOI) rose from 22.2% to 28.4%, and the rates of line ablation, peak heat release, and total heat release diminished by 19.8%, 71.7%, and 18.3%, respectively. This investigation provides a theoretical and empirical foundation for developing advanced flame-retardant polymeric composites.