Abstract: Based on the theory of the design of crack control and the crack control limit value, an equation to calculate concrete diaphragm wall's bending moment is deduced. Combining with the engineering example the discuss about the effect relationship between the reinforcement ratio and the limit bending moment and the load short term effect bending moment of underground diaphragm wall is made detailedly under w_lim=0.2 and w_lim=0.3, the conclusion of not only crack control requirement but also ultimate bearing capacity requirement can be met if you design the underground diaphragrn wall according to the theory of the design of crack control.