It is difficult to avoid the different depths of the main cell and arc cell of straight-web sheet pile cellular into the soil. Based on the engineering example，the mechanical characteristics of the structure with unequal main cell and arc cell length are analyzed，and the key and difficult problems in the calculation are put forward. The three-dimensional numerical model is established to calculate the stability，deformation，and stress of the straight-web sheet pile cellular seawall with unequal main cell and arc cell toe-levels，and the feasibility of reducing the depth of the arc cell sheet pile is analyzed. Combined with the engineering application，a new equivalent calculation method is proposed，which is using a two-dimensional model to calculate the sheet pile cellular seawall with unequal main cell and arc cell toe-levels. The research can be used as a reference for the popularization and engineering application of this structure.