To the crack monitoring of the carbon fibre reinforced plastics (CFRP) concrete composite arch, an experiment is conducted to monitor the appearance of the crack with bare fiber Bragg grating (FBG) strain sensors. The location of fiber Bragg grating (FBG) is determined via mechanic analysis, two kinds of pasting method is studied: local and distributed coupling (in the first case the measurement fiber is attached to the host structure at two points, in the second case the measurement fiber is attached along the whole active region). A comparison between the data of FBG and strain gauge is conducted to validate the precision and stability of FBG. The test results show the quantitative rule of crack initiation via K value standard deviation criterion. The initial cracking can be monitored by arranging the FBG sensors appropriately, good consistency can be achieved between FBG and strain gauge.