The good working state of cutoff wall is an important guarantee of the normal operation of earth-rock cofferdam on deep overburden. To understand the working state of cut-off wall on deep overburden in the presence of different materials, different setting positions, and different structural types, and to provide a reference for the structural design of cut-off wall, we conducted finite element calculation for the cut-off wall of an engineering project using ABAQUS software, and obtained the regularities of cutoff wall’s stress, displacement and deformation under different conditions. According to the obtained regularities, we proposed optimized design for the cut-off wall from qualitative and quantitative perspectives. Results reveal that plastic concrete cutoff wall is better than rigid concrete cut-off wall because the deformation of the former is more coordinated with cofferdam, which is conducive to the safety of the cofferdam. The position of cut-off wall has big impact on its own stress, displacement and deformation. Setting the cut-off wall 1/3 of weir bottom width away from the upstream weir feet is better than setting it at the local weir axis. When one single cut-off wall cannot meet the design requirements, we can consider using double cutoff walls, which could greatly increase the cofferdam’s safety margin.