Aiming at the calculation method of the minimum design water depth of seaport anchorage，the mathematical model is studied. The UNDERKEEL model is used to study the vertical motion of ships under the action of waves，and the outputs can provide the amplitude response operator （RAO） of the vertical motion of ships. In the study，the water depth of the anchorage is calculated according to 1.2~2.5 times of the ship's draft （T） with a step length of 0.05T as the input parameter，and the bottom touching probability of different types and grades of ships under the influence of different wave height and wave period is obtained. According to the selected allowable bottom touching probability，the parameter relationship between the minimum design depth of seaport anchorage and the ship's draft is obtained. Finally，relevant research methods and calculation formula of the minimum design depth of seaport anchorage are given，which can provide a reference for the design project of seaport anchorage，and can be used as a reference for the preparation of relevant design codes of seaport anchorage.