A highly active LaNi5-xAlx alloy films was prepared by using pulse electrolysis. The depolarization of Ni cathode and the co-electrodepositing principle in the molten salt system was studied by thermodynamic calculation and cyclic voltammetry, microscopic structures of alloy films were observed and analyzed by scanning electron microscopy and X-ray diffractometry. The results show the electrodeposition and diffusion processes are effectively separated by pulse electrolysis. In fact, the precipitation of aluminium in Ni cathode is found to significantly decrease the activity of La2O3 from Na3AlF6114g, Al2O31.2g and La2O34.8g molten salts firstly, then the depolarization of Ni cathode makes it possible for the co-electrodepositing principle of La and Al. Finally, the LaNi5-xAlx alloy films with high surface area and uniform composition is prepared, where x values rang between 3.5-4.