The present invention belongs to the field of ferric phosphate preparation, and provides high tap density ferric phosphate, a preparation method thereof, and lithium iron phosphate. The method includes following steps: (a) feeding a ferrous sulfate solution and a phosphate solution including hydrogen peroxide simultaneously into a first reactor for mixing and reacting to obtain nucleated ferric phosphate; wherein a molar ratio of iron element to phosphorus element in the feeding process is 1:1, and a stirring speed is 500-600r/min; (b) discharging the nucleated ferric phosphate to a second reactor for growth to obtain amorphous ferric phosphate slurry, and post-processing the amorphous ferric phosphate slurry to obtain the high tap density ferric phosphate; wherein a stirring speed is 120-150r/min. The first reactor is a small-volume reactor, and the second reactor is a large-volume reactor. The present invention solves the technical problems of high production cost of ferric phosphate, easy destruction of particle crystal structure, distortion of crystal lattice, and high impurity content, and achieves the technical effect of preparation of high tap density ferric phosphate at low production cost.