Abstract: The basic fluid-solid interaction formulas for a shell in fluid are given using elasticity theory of thin shells and fundamental equations of fluid mechanics. The united Lagrangian-Eulerian method is proposed and used to form the equations for the small bending of a cylindrical shell with a surrounding transverse flow, and then the velocity potential of the fluid field as well as the deformation and the internal force distribution of the shell are obtained. Using a specific example, the fluid field figures are obtained, and the effects of parameters on the deformation of the shell and pressure coefficient of the shell surface are discussed.