The invention relates to a barium titanate nanomaterial with a two-dimensional structure and a preparation method of the barium titanate nanomaterial. The preparation method comprises the following steps: adding a barium hydroxide water solution into a titanium oxide nano suspension solution, and uniformly stirring to obtain a mixed solution; taking the mixed solution to react for 1h to 10h under the conditions that the ultrasonic frequency is 20kHz to 25kHz, the power density is 30W/cm<2> to 100W/cm<2> and the temperature is more than 20 DEG C and less than 60 DEG C, so as to generate the barium titanate nanomaterial with the two-dimensional structure, wherein the mole ratio of barium atoms to titanium atoms is 1 to 1. The barium titanate nanomaterial with the two-dimensional structure, which is prepared by the method provided by the invention, is of a sheet-shaped structure; length and width sizes of the sheet-shaped structure are micron-grade, and a thickness size is a nano-grade. The preparation process of the barium titanate nanomaterial with the two-dimensional structure, provided by the invention, is simple and low in cost; meanwhile, the invention provides the barium titanate nanomaterial with the two-dimensional structure, which has excellent performances and a wide application prospect in the aspect of ultrathin energy-storage capacitors.