In order to improve the reliability and calculating speed of the maximizing shadow difference ( ) method in fault line selection, the principles of the maximizing shadow difference method and the differential filter algorithm are analyzed in detail, and a new fault line selection method of the maximizing shadow difference optimized by differential filter algorithm is proposed. The maximizing shadow difference method is optimized by differential filter algorithm. The optimized method avoids the intermediate referenced sine signal and reduces the multiplication calculation, which improves both the reliability and calculating speed. Theoretical analysis and simulation results show that the new method is immune to the parameters, such as the fault angle, transition resistance, fault distance, fault arc, and so on. The fault line selection accuracy rate can reach to 100%. This work is supported by Natural Science Foundation of Jiangsu Universities (No. 15KJD510006).