The stability of the slurry trench is very important in the construction of the underground diaphragm wall. In the current research, the local instability of the slurry trench is mainly investigated after the excavation of a unit slot is completely completed. However, the local stability in the process of excavation has received little attention. In this paper, the local stability in the process of excavation located in high permeability strata of diaphragm wall construction is investigated. A slurry infiltration experiment was carried out to investigate the distribution of the excess pore pressure in the high permeability strata, which can determine the effective support pressure. Then, the local stability of the slurry trench in the process of excavation located in high permeability saturated sand is calculated. The results show that the same types of sand according to the design code cannot be simply treated to have the same permeability and similar distribution of the excess pore pressure, since whether the filter cake can be formed and the quality of the filter cake are the key factors to determine the distribution of the excess pore pressure. This is also crucial for the local stability in the process of excavation located in high permeability saturated sand. It is suggested that attention should be paid to the local stability in the process of excavation located in high permeability strata when the slurry infiltration mode is the pure permeable zone.