In order to solve the problem that the ultimate displacement for the top of water cut-off linked pile is not determined so that the work of dewatering for the dock and monitoring for the cofferdam can’t be guided efficiently, the bending test and the compression test were carried out for the sample from water cut-off linked pile. The important material parameters such as tensile strength, compressive strength and elastic modulus were obtained. The methods of force analysis and formula derivation for linked pile were adopted. Farther more the material parameters were put into the formula to calculate the ultimate displacement for the top of water cut-off linked pile so that the safety of water cut-off linked pile was evaluate. The results showed that the ultimate displacement of the top of the secant pile is proportional to the failure stress and is inversely proportional to the elastic modulus and the maximum distance of the fiber from the neutral axis, so the elastic modulus should be controlled in a reasonable range.