To study the stress characteristics of deep water foundation steel cofferdams during construction, taking the 6# pier deep water foundation of Dingjiazhou Bridge as an example, finite element method ABAQUS software was used to establish a calculation model for single and double wall built-up structure steel cofferdams and traditional double wall steel cofferdams. The stress and deformation of different structural steel cofferdams were calculated, and the mechanical behavior changes of steel cofferdams were analyzed. The research results indicate that the stress situation of single and double wall built-up structure steel cofferdams is more reasonable compared to traditional double wall steel cofferdams. The weakest position of the entire structure occurs between two horizontal ring plates on the bulkhead concrete, and stress concentration is prone to occur at the position where the outer wall plate contacts the horizontal truss. However, the maximum deformation and stress values of the outer wall plate are 9.69 mm and 122 MPa, respectively, which meet the requirements of the specifications. In addition, by comparing the numerical simulation results with the on-site monitoring results, it can be seen that the numerical simulation results of each measurement point are basically consistent with the on-site monitoring results, with an error rate of less than 15%. The actual structure is more inclined towards safety, indicating that numerical simulation can accurately evaluate the mechanical behavior of single and double wall built-up structure steel cofferdams in actual engineering.