Abstract: In order to analyze the diagonal crack-induced-debonding of the fiber reinforced polymer (FRP)- concrete interface of FRP strengthened concrete beam ends more efficiently, a simple three-dimensional-nonlinear finite element model based on the ‘beam segment' between a beam end and the first diagonal crack was proposed. The difficulty to analyze the debonding stress by taking a whole strengthened beam with many cracks as a finite element model, therefore, was avoided. The proposed model was validated to be rational and reliable by the Saint-Venant principle and a numerical study. Based on this model, the distributions of the debonding stress under the influence of FRP stress levels, layers of FRP, the distance between the support and the first diagonal crack, and FRP-concrete bond-slip constitutive laws were analyzed. The numerical study results show a fairly good agreement with the existed experimental results.