Abstract: In order to simplify the calculation of the plane bending deformation of the beam,this paper deduces the calculation formula of the deformation of the beam by the method of the moment diagram area.When the beam bending stiffness is constant,and the moment diagram and bending moment graph easier to obtain,the corner and the deflection of any cross section of the beam can be solved without using the integral boundary condition at the bearing on the beam.Compared with the superposition method,there are also clear concept,the advantages of quick calculation.Practice shows that even if the distribution of the load on the beam makes the bending moment area and the centroid is not easy to be obtained directly.,A little promotion can easily solve the problem of the beam deformation.