The unmanned aerial vehicles with FUJIFILM X-T20 cameras were used for the imaging platform to got images of bridge cracks.Bridge crack shapes were identified by the bridge crack image processing program based on MATLAB.According to the shape feature，the short axis parameters of crack image area were selected as the parameters of resolution formula.The maximum crack width was calculated by revised resolution formula. Twelve images were selected to calculate the maximum crack width，and the average relative error of identifying crack width was 4.14%.According to the relationship between the crack width and the carrying capacity of the bridge，ANSYS model of the bridge was established to obtain the carrying capacity of the bridge corresponding to a series of crack widths. The crack width of concrete bridge is 0.6 mm when the excess coefficient of bearing rate is 0，with the crack width far exceeding the normal value.The excess coefficient of bearing capacity can be used as the key observation parameter of concrete bridge structure in the operation stage and it is of guiding significance to the long-term safety monitoring of concrete bridge.