Bentonite slurry wall is a new technology for seepage control and can be applied effectively for of dykes, embankment dams and their foundation. The trench is excavated under bentonite slurry supporting. Trench falure can be occured during excavation process. Therefore, the calculation of wall stability during trench excavation needs special attention. In this paper, the authors study the effects of three-dimensional, height of slurry fill and slurry density to the stability of the trench walls.