When the draghead excavates hard clay，the cutting resistance of the teeth is large，and the load of the main engine that needs to be matched is also increased correspondingly，which reduces the engineering economy. In order to analyze the value and change trend of the cutting resistance of the teeth in the cutting process of hard clay，and optimize the design and use of the draghead，we calculate the cutting resistance of teeth under multiple working conditions on the hard clay with a certain water content and standard penetration number，and calculate the length and width of soil damage during cutting by the calculation model. The results show that the horizontal cutting resistance of hard clay is greatly affected by the cutting depth，cutting angle and cutting width，and less affected by the cutting speed；when cutting hard clay，different types of teeth must be selected according to the actual working conditions. The cutting theoretical calculation model can be used for draghead design and construction process parameter optimization，which provides theoretical reference for the improvement of ship construction efficiency.