A health monitoring system for long span prestressed concrete box-girder bridges was designed to solve bridge safety problems related to structural cracks and excessive deflection. The hardware and software of system include 5 subsystems based on the damage mechanism and structural features of the bridges, the temperature monitoring subsystem, the deflection monitoring subsystem, the strain monitoring subsystem (including strains in critical sections of the bridge and widths of the main cracks of the bridge), dynamic property monitoring subsystem, and the wireless data transmission subsystem. Some proposals are provided for the health monitoring system design of box-girder bridges using monitoring results in situ.