The ternary-component NiCoAl-mixed metal oxides (NiCoAl-MMOs), which are expected to have a high capacitance, were successfully prepared as film electrode for capacitive deionization (CDI). Hexagonal NiCoAl-MMOs nanoplatelets with a lateral size between 250 and 400 nm densely covered the surface of the nickel foam substrate. With the optimal Ni/Co/Al ratio (1.5:1.5:1), NiCoAl-MMOs displayed a more well-distributed surface, better crystallinity, and higher specific surface area, while the Ni/Co/Al ratio of 1.5:1.5:1 was also optimal for the NiCoAl-MMOs film electrodes to achieve maximum capacitance of 1167 F/g. The NiCoAl-MMOs film electrodes possessed ideal pseudocapacitive behavior and good capacitive reversibility, and showed outstanding performance in CDI from the concomitant reconstruction of the layered double hydroxides by intercalating anions. The desalination capacity of the NiCoAl-MMOs film electrodes was 108.8 mg NaCl/g, which was significantly higher than that of binary-component NiAl-MMOs and carbon-based electrodes. The NiCoAl-MMOs electrodes were quickly regenerated by reversing the voltage, with a desorption rate of 81.36%. The electrosorption capacity was about 2.5 times higher than that of adsorption without bias, indicating that the intercalation of ions into NiCoAl-MMOs nanoplatelets was enhanced by applying an electric field. NiCoAl-MMOs showed great promise as a CDI electrode in desalination.