Abstract: River-crossing pipeline is threatened by flood which could induce the pipeline being eroded and exposed, moreover, floating in a large scale. Under the combined effects of dynamic water, buoyancy, gravity and resistance of bank soil, pipeline generally presents three-dimensional bending. A mechanical analysis model is built to investigate the mechanical behaviour of pipeline exposed in flood. Taking into account the nonlinear pipe-soil interaction, the axial force and material nonlinearity of pipeline steel, the dimensional bending curve and a deformation compatibility equation of pipeline are derived. And pipeline stress and strain are calculated with an iterative solving method. Based on the proposed analytical methodology, a computer program is developed and the pipeline deformation, stress and strain are analyzed through a series of examples. Each example is subsequently investigated with the finite element method and the calculation results of the proposed method are close to that of the finite element method. Finally, a safety assessment method for pipeline in flood is proposed according to limit state theory, by which the safety of a pipeline exposed in mountain torrent is assessed.