Abstract: In this paper, the coverage area of metal surface cracks was detected based on C-scan mode by using flexible Koch fractal eddy current sensor and traditional flexible circular parting eddy current sensor. The experimental results showed that cracks with a length greater than or equal to 3 mm can be effectively identified by C-scan. Among them, compared with the traditional flexible circular fractal eddy current sensor, the signal attenuation detected by the flexible Koch type eddy current sensor was small, and the phenomenon of missed detection was not easy to occur, and the detection of small cracks was particularly obvious.