The electrical potential technique was applied to monitor the crack initiation and propagation in LY12-CZ plates. The feasibility of this method was validated by a simulation experiment firstly. Then fatigue crack monitoring experiment based on LY12-CZ aluminum alloy center-hole plate specimen was carried out. After a special coating sensor was prepared on the monitoring area of the specimen by surface technology, a set of fatigue crack monitoring experiments were carried out. The changes in the potential values of the coating sensor resulting from crack damage were documented. Since the property of the coating sensor and the introduced current were constant, the measured voltage values would only relate to the crack’s length and position. Based on the experimental results, the relation curves between voltage values and crack lengths were obtained, and a set of empirical formulae were deduced.