There are huge amount of short and medium-span bridges in transportation system and their collapse occurs frequently.How to reasonably design a structural health monitoring system for short and medium-span bridges has become a major demand in traffic engineering. Considering the engineering requirements of bridge monitoring， this paper deeply analyzes the difference be‐tween the monitoring requirements of short and medium-span bridges and large-span bridges， and puts forward the lightweight design concept of the structural health monitoring system for short and medium-span bridges for the first time. The lightweight design method and process including input monitoring， output monitoring and system calibration are systematically constructed. The supporting theories including system identification theory， structural analysis theory and load carrying capacity evaluation theory are detailed. At the end of the paper， a preliminary outlook for the future development of the method is given. This method provides a practical idea for standardizing the structural health monitoring technology of short and medium-span bridge， and promotes the practical process of intelligent bridge management.