The invention relates to a core shell structure n - titanium dioxide @ p - cobalt titanate nanocrystalline thin film and a preparing method thereof. A clean substrate is installed on a sample stage of a magnetron sputtering device firstly, and a CoTiO3 target and a TiO2 target are installed at two radio frequency target positions of the magnetron sputtering device correspondingly; a sputtering film coating chamber of the magnet control sputtering device is vacuumized and injected with inactive gas, and gas pressure of the sputtering film coating chamber is kept at 0.1Pa - 2Pa; the CoTiO3 target is pre-sputtered for 5min - 15min; the substrate is heated up to 300 DEG C - 600 DEG C and is subjected to heat preservation, sputtering of the CoTiO3 target is started for 30min - 90min, and a CoTiO3 orderly nanocrystalline thin film is obtained; and the CoTiO3 orderly nanocrystalline thin film is adjusted to be parallel with the TiO2 target, the TiO2 target is sputtered for 10s - 120s, and the core shell structure n - titanium dioxide @ p - cobalt titanate nanocrystalline thin film is obtained. According to the core shell structure n - titanium dioxide @ p - cobalt titanate nanocrystalline thin film and the preparing method thereof, appearance of the thin film can be adjusted effectively, the film-forming property is good, operation is convenient, the producing period is short, efficiency is high, and the core shell structure n - titanium dioxide @ p - cobalt titanate nanocrystalline thin film and the preparing method thereof are suitable for industrial production.