Abstract: Based on the Coulomb’s concept that the earth pressure against the back of a flexible retaining wall with drum deformation was a thrust exerted by the sliding soil wedge formed by the back of the wall and a plane passing through the bottom edge of the wall with an angle of inclination θ.The differential equation of the first order was set up by the equilibrium of forces on the horizontal layer taken out from the wedge.The theoretical formulae of the unit earth pressures,the resultant earth pressures and the points of application of the resultant earth pressures on the flexible wall were obtained for the drum movement mode.The comparisons were made among the formula presented here,the Coulomb’s formula and some experimental observations.It was demonstrated that the magnitudes of the resultant earth pressures for the drum movement mode were equal to those determined by the Coulomb’s theory,but the distribution of the earth pressure and the points of application of the resultant earth pressures were significantly different.Soil arching altered the distributions of pressure on the flexible wall.Finally,some factors that have influences on the magnitude and distribution of earth pressures,such as soil properties,frictional characters between walls and soils,position of the maximum deformation of the walls were studied.