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All‐inorganic CsPbX3 (X = Cl, Br, or I) perovskite thin films are attractive emissive layers for high‐performance light‐emitting diodes (LEDs) due to their precisely tunable bandgaps, excellent color purities, good stabilities, and solution processabilities. However, the fabrication of high‐quality CsPbI3−xBrx thin films is very challenging because the crystal growth of mixed halide CsPbI3−xBrx is in low controllability. Herein, a synergetic regulation strategy using fluorine polymer (Poly(vinylidene fluoride‐co‐hexafluoropropylene)) and a small amino acid molecule (L‐Arginine) is developed to fabricate high‐quality CsPbI3−xBrx thin films for efficient pure red perovskite LEDs. In the fabricated CsPbI3−xBrx thin film, the fluorine polymer plays a crucial role in confining CsPbI3−xBrx crystal size at the nanoscale and the small amino acid molecule acts as a passivation agent to reduce the trap‐state density. Under this synergetic effect, a uniform CsPbI3−xBrx thin film with a high photoluminescence quantum yield up to 40% can be obtained to fabricate an efficient pure red perovskite LED with a maximum external quantum efficiency of 4.5% and a maximum brightness of 3100 cd m−2. The reported synergistic regulation strategy will open a new avenue to fabricate efficient pure color CsPbX3 perovskite LEDs. [ABSTRACT FROM AUTHOR]