Abstract: This study aims to investigate the fatigue life and failure mechanism of hybrid integrated circuit(HIC) encapsulation shells fabricated using parallel seam welding under random vibration loads, providing theoretical support for their fatigue design and optimization. First, encapsulation shells were prepared by welding 10 steel bases with 4J42 alloy covers using parallel seam welding technology. The welding quality was verified through microstructure analysis, revealing uniform structures, smooth transitions, and no obvious macroscopic defects in the weld zone. Subsequently, random vibration tests were conducted, and failure modes were determined through fracture surface analysis. The results showed that when the random vibration loading direction was perpendicular to the cover plate and the vibration level reached 25 g, fatigue failure occurred in the weld zone at the middle of the long edge of the cover plate, with cracks initiating at the weld edge and propagating along the thickness of the cover plate. Additionally, sinusoidal vibration tests were performed, and finite element analysis was conducted using ABAQUS to calculate the stress response at critical locations, based on which an S-N curve of the encapsulation shell was constructed. Finally, stress frequency-domain data under random vibration were transformed into time-domain data using inverse Fourier transform, and the fatigue life was predicted using the rain-flow counting method and linear damage accumulation law. The results indicated that the fatigue life of the encapsulation shell under a 20 g random vibration load was approximately 37.69 hours.