A method is presented to estimate the remaining life of a moving power cable online. The cable is monitored online remotely for further providing suggestions to users for reducing times of power failure and economic loss. An offline AC impedance measurement experiment is designed at first. Three artificial neural networks are established for convert measured impedances into impedances under a baseline context to calculate impedance change ratios. The impedance change ratio indicates the damage of the cable. At last, a remaining margin of the impedance change ratio is figured out online under various contexts with three equations. Thus, the remaining life of the cable is obtained online.