Bridge deflection response is one of the most important indicators used for structural condition assessment of bridges. There are currently more methods and devices for deflection measurement, but they cannot be better satisfied in terms of economy, applicability and measurement accuracy. This paper proposes a rapid and highly accurate method for measuring mid-span deflection on small and medium span bridges. Relying on the high accuracy of displacement transducers in direct contact measurement, an auxiliary measurement device is developed to transfer the deflection of the measurement points on the bridge to the displacement transducer in the form of a rigid connection, thus achieving accurate and dynamic testing. A coupled vehicle-bridge-testing system model is developed to calculate the displacement deviation between the bridge measurement point and the monitoring point under vehicle loading, as well as a model experiment simultaneously, to verify the feasibility of the method for dynamic response testing. The results show that the measurement deviation caused by the lateral wind load is less than 5%, which can be neglected in practical application, proving that the test method has high testing accuracy and practicality.