To investigate the dynamic stability of cantilever intake pipes conveying internal flow， a bidirectional fluid-structure interaction (FSI) model was developed and validated against experimental data from literature. Results demonstrated that exceeding a critical flow velocity triggered first-mode flutter instability， characterized by hybrid vibrations combining large-amplitude flutter and small-amplitude buffeting oscillations. Displacement peaked at the free end while strain energy concentrated near the fixed end， with periodic fluctuations revealing unsteady fluid-structure energy exchange. Flow-field analysis identified intense suction at the inlet， inducing flow acceleration and pressure drop within the Kuiper-corrected negative-pressure range. Asymmetric vortex shedding synchronized with structural vibration was observed， potentially generating periodic lateral excitations. Compared to spatially sparse experimental measurements， the bidirectional FSI approach captured full-field， time-synchronous coupling data， elucidating energy transfer pathways from flow separation and vortex shedding to structural response. This methodology bridges experimental gaps through high-resolution field visualization and adjustable parameters， providing a robust foundation for advanced flow-induced vibration research.