A method of preparing lithium transition metal phosphate, the method comprising: feeding reactants comprising lithium, a transition metal, and phosphoric acid into a reactor, and mixing the reactants in the reactor, wherein the reactor is a high gravity rotating packed bed reactor comprising: a chamber that defines an inner space; a permeable packed bed that is rotatable, is disposed inside the chamber, and is filled with a porous filler; at least one source material feeding line through which the reactants are fed into the inner space; and a slurry outlet through which a slurry is discharged from the inner space; and generating a crystal nucleus by chemically reacting the reactants in the reactor, wherein a centrifugal acceleration of the permeable packed bed is in a range of 10 to 100,000m/s 2, an inner temperature of the reactor is maintained in a range of 0 to 90°C, and a retention time of the reactants in the reactor is in a range of 1 ms to 10s, wherein the chemical reaction is an acid-base reaction, wherein the reactants comprise an acidic source material and a basic source material, wherein the acidic source material is fed into the reactor through a first source material feeding line and the basic source material is fed into the reactor through a second source material feeding line, wherein a) the acidic source material includes lithium chloride, a transition metal chloride, and H 3 PO 4 and the basic source material includes an inorganic base; or b) the acidic source material includes transition metal chloride and H 3 PO 4 and the basic source material includes lithium hydroxide; or c) the acidic source material includes lithium chloride and H 3 PO 4 and the basic source material includes a transition metal hydroxide; or d) the acidic source material includes H 3 PO 4 and the basic source material includes lithium hydroxide and a transition metal hydroxide. a chamber that defines an inner space; a permeable packed bed that is rotatable, is disposed inside the chamber, and is filled with a porous filler; at least one source material feeding line through which the reactants are fed into the inner space; and a slurry outlet through which a slurry is discharged from the inner space; and generating a crystal nucleus by chemically reacting the reactants in the reactor, wherein a centrifugal acceleration of the permeable packed bed is in a range of 10 to 100,000m/s 2, an inner temperature of the reactor is maintained in a range of 0 to 90°C, and a retention time of the reactants in the reactor is in a range of 1 ms to 10s, wherein the chemical reaction is an acid-base reaction, wherein the reactants comprise an acidic source material and a basic source material, wherein the acidic source material is fed into the reactor through a first source material feeding line and the basic source material is fed into the reactor through a second source material feeding line, wherein a) the acidic source material includes lithium chloride, a transition metal chloride, and H 3 PO 4 and the basic source material includes an inorganic base; or b) the acidic source material includes transition metal chloride and H 3 PO 4 and the basic source material includes lithium hydroxide; or c) the acidic source material includes lithium chloride and H 3 PO 4 and the basic source material includes a transition metal hydroxide; or d) the acidic source material includes H 3 PO 4 and the basic source material includes lithium hydroxide and a transition metal hydroxide. a) the acidic source material includes lithium chloride, a transition metal chloride, and H 3 PO 4 and the basic source material includes an inorganic base; or b) the acidic source material includes transition metal chloride and H 3 PO 4 and the basic source material includes lithium hydroxide; or c) the acidic source material includes lithium chloride and H 3 PO 4 and the basic source material includes a transition metal hydroxide; or d) the acidic source material includes H 3 PO 4 and the basic source material includes lithium hydroxide and a transition metal hydroxide.