To address the issue of reduced output reliability of boron/potassium nitrate igniters caused by KNO₃ hygroscopicity， a dual coating modification strategy based on an in-situ reaction and a solvent-antisolvent method was proposed. Firstly， a copper stearate （CuSt₂） coating layer was constructed on the KNO₃ surface via in-situ reaction between stearic acid and copper acetate. Secondly， the trifluoroethylene-vinylidene fluoride copolymer （F₂₃₁₄） was coated on KNO₃@CuSt₂ using the solvent-antisolvent method to prepare CuSt₂/F₂₃₁₄ double-coated KNO₃. Finally， the double-coated KNO₃ was uniformly mixed with boron at a mass ratio of 3∶1 to obtain the formula-optimized B/KNO₃@CuSt₂@F₂₃₁₄ igniter， aiming to synergistically regulate the hydrophobic properties and reaction activity of the igniter. Scanning electron microscopy （SEM）， Fourier transform infrared spectroscopy （FT-IR）， X-ray photoelectron spectroscopy （XPS）， and inductively coupled plasma spectroscopy （ICP） were employed to confirm the sequential coating of CuSt₂ and F₂₃₁₄ on KNO₃ particles. The hydrophobicity of the samples was characterized using a contact angle measurements. The effects of modified KNO₃ on the thermal reaction and combustion performance of the igniter were evaluated by thermal analysis and laser ignition experiments. The results demonstratieded that the hydrophobic performance of CuSt₂@F₂₃₁₄ double-coated KNO₃ was superior to that of single-coated KNO₃with CuSt₂ or F₂₃₁₄ （the water contact angle of uncoated KNO₃ was 0°）. When the proportions of CuSt₂ and F₂₃₁₄ dual coating layers were 6% and 2%， respectively， the comprehensive performance of KNO₃@6%CuSt₂@2%F₂₃₁₄ and its boron-based igniter was optimal. The water contact angle of KNO₃@6%CuSt₂@2%F₂₃₁₄ increased to 95.8°， and the heat release of B/KNO₃@6%CuSt₂@2%F₂₃₁₄ reached 3200.67 J·g^-1， which was 23% higher than that of B/KNO₃ igniter （2601.69 J·g^-1）， while the onset temperature of the thermal reaction decreased by approximately 23 ℃. Laser ignition tests showed that compared with the unmodified B/KNO₃ igniter， the B/KNO₃@6%CuSt₂@2%F₂₃₁₄ igniter exhibited a shorter ignition delay time， stable flame propagation， and reliable laser ignition performance. This study realizes the synergistic enhancement of hydrophobicity and reaction activity in the B/KNO₃@6%CuSt₂@2%F₂₃₁₄ igniter by constructing a dual coating layer on the surface of KNO₃， providing a new approach for improving the performance of high-reliability boron/potassium nitrate igniters.