Abstract: A damping ratio identification method of the simply supported beam based on the vehicle bridge coupling dynamics theory is proposed. Firstly, the test vehicle is designed as a single degree of freedom system according to the dynamic theory, and then the signal of the simply supported beam bridge response is obtained from the response signal of the contact point between the test vehicle and the simply supported bridge by using the sensor installed on the test vehicle. The signal including the first-order frequency of the simply supported beam bridge is filtered based on the principle of vehicle bridge coupling dynamics. Finally, the damping ratio of the simply supported beam bridge is assumed, The assumed first-order vibration mode of the simply supported beam bridge is obtained through the assumed damping ratio of the simply supported beam bridge, and the cycle is continued until the maximum value point of the first-order vibration mode calculated under the assumed damping ratio is in the middle, that is the identified real damping ratio of the simply supported beam bridge. This paper first explains the feasibility of this method from the theoretical derivation of vehicle bridge coupling dynamics, and then analyzes the vehicle bridge coupling dynamics model under the influence of different vehicle speed and unsteady vehicle speed, road roughness, environmental noise and other factors. Finally, it is preliminarily verified by real bridge test. The results show that this method can overcome the influence of external adverse factors to a certain extent, achieve the purpose of identifying the damping ratio of beam bridge, and provide a better method for identifying the damping ratio of simply supported beam bridge. It has the advantages of less parameter setting, simple and convenient operation and higher test accuracy, At the same time, it is helpful to promote the practical engineering application of the vehicle bridge coupling dynamics theory and technology based on vehicle bridge coupling in beam bridge modal parameter identification.