Abstract: When the flexible eddy current array sensor was integrated to monitor cracks in metallic bolt hole edge, the sensor would suffer assembly stress and working stress from the metallic structure. In order to increase durability of the sensor, the failure mode and mechanism in monitoring cracks were investigated by finite element stress analysis and crack monitoring experiment. It was shown that the cracks and coil wire fracture would appear in the sensor corresponding to crack zone of metallic structure, and the propagation trend of crack in the sensor is similar to the crack in the metallic structure. It can be concluded that the static friction force between the sensor and the metallic structure, and the stress and distortion in crack zone of metallic structure lead to the failure of the sensor.