Abstract: The astronomy-storm tide in the Bohai Sea was modeled by using three-dimensional model and data from 82 selected strong weather processes.The model was tested with real observation data,and satisfactory results were obtained.Form the astronomical highest (lowest) tide levels,the extreme high(low) water levels of multiyear return periods and the extrerne-storm set-up (set-down) of multiyear return periods,which were obtained by the yearly extreme high(low) water levels and the yearly extreme storm set-up(set-down) observed at the coastal hydrographic stations,A linear combination formula for calculating the extreme water levels of multiyear return periods at 5 typical areas in the Bohai Sea is established.The formula can be used in the design of marine engmeeenng projects.