The disturbance is, in layman’s terms, the amount of deformation. The disturbance of the steel structure such as the cantilever beam should meet the corresponding specifications. The deformation should not be too large, and the formula of the material mechanics can be used for calculation. The deflection of the bridge has a corresponding relationship with the corner angle of the section. The deflection of the bridge can be measured by a double-axis inclination sensor mounted on the bridge. The method uses the structural finite element model to calculate the deflection curve of the unit load acting at different positions. The deflection curve is used as the reference displacement mode, and the true deflection is the linear combination of the reference displacement modes. The combination coefficient is determined by using the minimum inclination test data. The method of two-square fitting effectively reduces the influence of test errors.