Abstract: To measure surface cracks in conductor, test samples are made to simulate natural defects by 3-point bending test. The crack growth behavior in material is achieved after comparing and studying the measurement of surface cracks using electric potential drop method. The results show that the precision of measurement is about 0.1 mm for cracks in steel alloy, while it is not good for aluminium alloy because of the accretion of cracks, it makes the value smaller than the actual, but the measuring error is less than 20%.