On the basis of the previous damage severity identification method of steel truss bridges, two damage severity identification methods of simply supported beam bridges are presented: correlation coefficient method and modal assurance criterion method of global mode shapes. Based on a simply supported beam model in the laboratory, both experimental and numerical simulation results under pulse excitation indicate that the proposed methods can identify the damage severity of damaged elements accurately and they have strong anti-noise-interference ability. Moreover, the effect of different excitation on results is examined in the methods; all of these lay a good foundation for engineering.