The paper chiefly deals with the given method of the characteristic time and fluid boundary condition in the analysis course of the fluid-solid couple

which is applied to analyze the couple of fluid-solid of the cofferdam of Tai’an Pumped Storage Power Station. At the same time

it studies the influence of the foundation excavation on the stability of the cofferdam and the slope of the foundation. For the sake of giving the fluid-flow boundary and the proper characteristic time in the excavating process

the last result makes clear the distinct drop of the pore pressure in the cofferdam and foundation. The reason is

firstly

the enlargement of fluid-flow boundary after the excavation and

secondly

the lengthenment of the fluid-flow time in the computation. Those indicate the importance of the characteristic time and fluid boundary in the course of the fluid-solid couple analysis.