Abstract: The key to ensure the safety and reliability of structure is to find the fatigue cracks origination in time and monitor its propagation effectively. The shortcomings of the traditional crack detection methods were analyzed, and the electric potential method was pointed out to be suitable for fatigue crack monitoring. The principle of electric potential method was introduced, and a set of experiments with aluminium foil films were carried out. Based on the experimental data, a set of relation curves between voltage values and cracks lengths were obtained on condition that those cracks grew at several different positions, and from these curves it could be seen that it was feasible to monitor fatigue cracks using electric potential method.