In the trailing suction hopper dredging, mechanical cutting methods are widely used to loosen the hard sedimented soil on the seabed. It is of great importance to find some effective techniques for higher soil loosening efficiency, so it is a key issue to study the mechanism of soil cutting resistance. A new experimental setup with monitoring system was developed in the tests to represent whole cutting process of the bed soil by a prototype draghead tooth. The experiments were conducted to investigate the large deformation / failure process and the pore water pressure response at the tooth-soil interface during the draghead tooth cutting of the fine sandy soil from Huanghua port, close to coast of the Bohai Sea in North China. The experimental results show that the intact soil ahead of the rake teeth was squeezed, cut and subjected to shear deformation. In the much short time of soil cutting process, the effective stress and deformation of the soil should be considered under undrained condition; and the pore water pressure decreased significantly due to the effect of soil shear dilation. The soil cutting resistance of the draghead tooth came from the increased effective soil stress which resulted from the significant decrease of the pore water pressure in the soil.