Magnetic flux leakage inspection is one of the most common nondestructive techniques used to detect crack-like defects in ferromagnetic materials. In order to improve the accuracy and reliability of crack detection, sensors based on the giant magneto-impedance (GMI) effect are suitable candidates for the magnetic sensors used in MFL detection systems. In this paper, we have introduced a double-core GMI sensor based on Co-based amorphous wires for the detection of rectangular shaped surface cracks. A theoretical method compared with experimental measurements indicates that an increase in the crack dimension is observed via an increase in the sensor signal amplitude. Magnetic imaging of different cracks shows that there is a good correlation between the size and position of cracks and the sensor signals; which can lead to improvement of the MFL test industry.