In response to the potential large settlement and instability issues of deep soft soil foundation under the vertical breakwater,based on a certain vertical breakwater project with deep soft soil ground,combined with natural conditions,structural safety requirements,cost and construction period limitations,we discuss the selection of foundation treatment methods,the layout,pile diameter,replacement rate,depth of the cement mixing pile,and construction technology key points.By the method of combining theoretical analysis with engineering experience,it is concluded that under the premise of reasonable control of key parameters and taking appropriate measures to improve construction quality,the improvement method of supporting grid-shaped small-diameter cement mixing piles combined with flexible cushion layers is feasible and relatively economically reasonable for the deep soft soil foundation under the vertical breakwater.