To adapt to the trend of increasing miniaturization and high integration of microelectronic equipments, there is a high demand for multifunctional thermally conductive (TC) polymeric films combining excellent flame retardancy and low dielectric constant (ε). To date, there have been few successes that achieve such a performance portfolio in polymer films due to their different and even mutually exclusive governing mechanisms. Herein, we propose a trinity strategy for creating a rationally engineered heterostructure nanoadditive (FG@CuP@ZTC) by in situ self-assembly immobilization of copper-phenyl phosphonate (CuP) and zinc-3, 5-diamino-1,2,4-triazole complex (ZTC) onto the fluorinated graphene (FG) surface. Benefiting from the synergistic effects of FG, CuP, and ZTC and the bionic lay-by-lay (LBL) strategy, the as-fabricated waterborne polyurethane (WPU) nanocomposite film with 30 wt% FG@CuP@ZTC exhibits a 55.6% improvement in limiting oxygen index (LOI), 66.0% and 40.5% reductions in peak heat release rate and total heat release, respectively, and 93.3% increase in tensile strength relative to pure WPU film due to the synergistic effects between FG, CuP, and ZTC. Moreover, the WPU nanocomposite film presents a high thermal conductivity (λ) of 12.7 W m