The study proposes the optimized line-type of a reusable floating arch cofferdam creating the dry area to reinforce the dangerous dam. The water is discharged from the cavity of the arch cofferdam which automatically rises in the water, and then pulls to the next construction site. So the linetype of floating arch cofferdam need optimize in order to reduce the engineering quantity but enough strength. The study estimates the force performance, the deformation at the support and the engineering quantity of five schemes using CAD and SAP software. The schemes respectively are the semicircle , single center circle that the center angle is 140°, elliptical arch, and two three-center's circle. The final conclusion is that the semicircle is preferred for surrounding a dam section, and the three-center circle(60°) is preferred for surrounding more than two dam section. The floating cofferdam has practical application value, and the structure of the floating arch cofferdam is innovative.