Steel cofferdam is an advanced technology for high pile cap construction in deepwater foundation. Using Xiangjiang river bridge of Changsha-Xiangtan expressway as engineering background, we use software ANSYS to analyze the stress states of sealing bottom concrete layer of steel cofferdam of this bridge, and obtain some results of deformation, direct stress, principal stress, shear stress and equivalent stress. At the same time, a fixed-ends beam under uniform pressure is used to simplify the analytical model, and results show that this model can give relatively correct stress state with proper precision, but give poor deformation state. As for the design of steel cofferdam, engineers are mainly interested in the stress results. So the simplified model can be used in the design and analysis procedure.