This study investigates the multi-hazard vulnerability of a high-pier bridge under combined flood effects. A Gaussian regression surrogate model was developed based on finite element (FE) simulations, and multidimensional stochastic analyses were performed using Monte Carlo and Latin hypercube sampling methods. The flow amplification factor (λ), representing hydraulic disturbance, and a scour depth prediction model were introduced to evaluate the variation of bridge failure probability under different flood intensities.Results show that hydraulic actions significantly increase the failure probability across multiple failure modes. An average 5% increase in flow velocity leads to a maximum rise of 8.3% in failure probability, while the dynamic scour process reduces the flood intensity threshold by over 30%. These findings indicate that bridges are more prone to failure under high-velocity and shallow-water conditions. Furthermore, the influence of vessel collision under scour conditions was examined using fragility curves with vessel velocity as the intensity measure (IM). Increasing scour depth shifts the curves leftward, reducing structural impact resistance; when the scour depth increases from 2 cm to 8 cm, the probability of moderate damage rises from 0.028 to 0.442.This study elucidates the coupled effects of flood, scour, and vessel collision on bridge performance, providing a scientific basis for vulnerability assessment and risk-informed design under extreme hydraulic conditions.