Abstract: For the internal force of diaphragm, the formulae of plastic calculation in comparatively weaker ground and the calculation method of adjusting the internal force by applying axial force on the brace are presented; in better ground the formula of elastic calculation is adopted.For the embedment depth of diaphragm, two theoretical formulae of considering the wall resistance moment in various soil condition or considering both the cohesion c and internal friction angle φ of soil mass, and a semiempirical formula based on the data of model test are presented.