Aeronautical flared tube fittings are widely used in aircraft hydraulic, fuel and pneumatic systems for pipeline connections and sealing. These fittings frequently experience fluid leakage under vibration conditions, with transversal vibration being the primary cause of thread loosening and seal failure. This paper establishes a coupled analysis framework integrating vibration behavior, microscopic contact characteristics, and leakage rate calculation for flared tube fittings. The study systematically reveals the contact stress distribution and leakage evolution at sealing interfaces under transversal vibration. Results indicate that transversal vibration transforms uniform circumferential contact pressure into non-uniform distribution, reduces contact area, and expands leakage channels on the vibration-direction side. After 10 vibration cycles, leakage rate increases to 2.68 times initial value. The research quantifies leakage variations under different bolt preloads, vibration amplitudes, surface roughness levels, and medium pressures. Design recommendations propose minimum preload force of 4180 N, maximum surface roughness of 1.6 μm, and clamp installation near fitting connections to mitigate vibration effects.