In order to interpret the real stress characteristic, construction stage of double-wall steel sheet pile cofferdam in dock is simulated by the soft of PLAXIS. The displacement of cofferdam, the internal force steel sheet piles and tie rods, and the safety factors are obtained. The undrained case in the construction stage and the drained case in the serviceable stage are also considered. This numerical analysis results are comprehensive and reflect the limitation of the conventional method. The designers should pay attention to this. This method agrees well with the practical engineering, thus may serve as a reference for similar projects.