Due to the need to provide a larger working space in the pit of the ship lock near the water，the cement mixing pile is often used as the supporting structure. Steel sheet piles are mostly used as temporary water-retaining cofferdams outside the foundation pit. Taking the foundation pit of a ship lock as an example，we analyze the influence of temporary mixing cofferdams on steel sheet piles during the construction of cement mixing，and obtain the variation law of soil pore pressure during the construction of mixing piles through the field pore water pressure test，based on which a solution for excessive deformation of the cofferdam is proposed. According to the field pore water pressure test，we obtain the variation law of soil pore pressure in the depth and width of the mixing pile construction process and the influence range of the cement soil mixing pile construction on the surrounding，and propose a solution for the excessive deformation of steel sheet pile cofferdam. This study can provide a reference for the design and construction of similar foundation pits.