The structural damage of the bridge is normally a local phenomenon. The vehicle trespassed the local damage induces a local response, which is much sensitive to the damage. The bridge subjected to a moving vehicle is a time-varying process. The local damage in a region trespassed by the vehicle can be accurately identified by the time-varying characteristics of the bridge response. The synchrosqueezing transform is a kind of reassignment method to sharpen the time-frequency representation and it is an efficient tool to decompose the non-stationary signal into different components. A novel method based on multi-synchrosqueenzing transform is proposed to extract the time-varying characteristics of the vehicle-bridge interaction systems for bridge structural health monitoring. A vehicle-bridge interaction model is built to simulate the bridge under moving vehicles. The effect of bridge parameters, the vehicle speed on the time-varying characteristics of the vehicle-bridge interaction system is studied. Numerical results show that the proposed method is efficient and accurate to extract the time-varying features of the vehicle-bridge interaction system, which could be potential indicator of bridge damage.