According to Fuchunjiang river lock reconstruction project,we probe into the diversion standard for the medium-high-head hydraulic lock’s cofferdam expansion project,the overall layout and structural design from the design point.Under the prerequisite of satisfying the demand of flood-control,power generation and channel variation,we determine the dry season flood control level of the cofferdam.Combining with the arrangement of the lock’s hydraulic structure,we optimize the overall layout scheme for the cofferdam,and propose overfall cofferdams of different structural types for different sections of cofferdam,to serve new design ideas and train of thought for the design of similar high-head lock reconstruction project’s cofferdam,and add new features for the cofferdam engineering.