Based on the study background for structural health monitoring (SHM), fiber Bragg grating (FBG) sensor is researched. The study on FBG starts and matures in the field of telecommunication, and the corresponding study in the field of civil engineering is in a development stage even. To improve its further developments and promote its application in engineering, two kinds of quasi-distributed FBG sensors placements are considered, one for the fiber reinforced plastics (FRP) package and the other for without package. The sensors are pasted on the bottom of the beam. Study on the detecting effectiveness and damaqe locating of the quasi-distributed FBG sensor when the reinforced concrete beam specimen cracks appear are carried out. The experimental results show that the crack can be roughly located, and the strain sensitivity of the FBG sensor with FRP package declines relative to the rare FBG sensor.