This paper describes the structural design,performance test and appli cation of a surface-mounted FBG strain sensor for the load test of a highway bridge.A stainless steel packaged elastic structure with the capacity of strain sensitization and adjustment is proposed.An FBG is mounted in the cylinder located in the center section of the sensor.The cross sectional area of the center cylinder is smalle r than that of other parts of the sensor.The magnification factor of strain measurement could be adjusted by changing the len gth and cross sectional area of the center cylinder,which is the basic principle of the sensitization.A refere nce test method is also designed for the calibration of the strain sensor.The strain measurement test results are consi stent with the theoretical calculation. After each calibration test,24FBG strain sensors and 6FBG tempera ture compensation sensors are installed on the undersurface of box girder of Dia o shui yan bridge in Yongtaiwen highway.The strain sensors demonstrate excellent measurement capability in a series of load tests.S train responses of the strain sensors under three static working conditions and three dynamic working conditions are o btained effectively and plotted clearly,which demonstrate a more extensive appli cation promising.