The invention provides a preparation method of high-density nanometer barium titanate ceramics. The method comprises the following steps: 1) at the room temperature, pressing nanometer barium titanate powder into a sheet with a steel die on a tablet machine under a pressure of 8 Mpa in a one-way pressurization manner, and maintaining the pressure for 6-10 min; 2) performing annealing to the sheet pressed in the step 1); and 3) taking the nanometer barium titanate sheet sample out of an annealing furnace, packing the sample with a silver foil, putting the packed sample in a boron nitride tube, putting the boron nitride tube in a hollow graphite column, blocking the two ends of the boron nitride tube with boron nitride columns, putting the hollow graphite column in a pyrophyllite block provided with holes, putting a graphite sheet and a molybdenum sheet at two ends of the hollow graphite column, in sequence, blocking the holes of the whole pyrophyllite with a steel ring packed with an aluminum foil, wherein pyrophyllite is taken as a pressure-transmitting medium and the hollow graphite column is taken as a heating furnace, putting the packed pyrophyllite in a hexahedron anvil press for hot press processing, and taking the sample out after hot press is completed to obtain the compact nanometer barium titanate ceramics.