Aiming at the complicated calculation of the double-row steel sheet pile cofferdam structure in deep silt foundation, the calculation formula of safety and stability was obtained from the aspects of anti-shear deformation stability, bottom heave-resistant stability, overall anti-sliding stability, anti-overturning stability and overall sliding stability under operating conditions based on the soil mechanics theory. In addition the minimum penetration depth of the steel sheet pile was given with mathematical theory. Taking a double-row steel sheet pile cofferdam project in Zhejiang Province as an example, according to the calculation formula proposed in the present paper, the recommended value of the minimum penetration depth is 17. 01m, which is basically consistent with the actual design value of 18. 50 m. Numerical simulation based on FEM was also performed and the calculated data of the double-row steel sheet pile was closer to the measured value. Comparison with actual horizontal displacement data shows that the double-row steel sheet pile cofferdam structure design is reasonable and reliable, providing reference for related engineering applications.