Based on the basic assumptions of pure bending damage of beams，a simple bending damage theory is proposed, in which the definition of bending damage variable is defined by reduction of moment of inertia similar to that of tensile damage variable by reduction of loading area by L. M. Kachanov (1958). For simplicity of application in engineering, the evolution law of bending damage variable can be adapted as a simple form. As an example, an exact bending damage analysis of a beam for creep pure bending is made. The calculating results are compared with the results obtained by Kachanov's tensile damage theory (1986). Moreover, in addition to determination by experiments (similar to the measurements of tensile damage, J. Lemaitre, 1987)，the material's constants of the simple bending damage model can be determined in first approximation to Kachanov's tensile damage model.