The invention provides a cerium oxide crystal preparation method, which comprises: 1, respectively adding ultrapure water to an organic acid, a cerium salt and a carbonate, dissolving, and diluting toobtain an organic acid solution, a cerium source aqueous solution and a carbonate aqueous solution; 2, mixing and stirring the organic acid solution and the cerium source aqueous solution, adding thecarbonate solution under stirring, and carrying out a precipitation reaction to obtain a cerium carbonate precipitate; and 3, collecting the cerium carbonate precipitate, and carrying out high temperature calcining to obtain the cerium oxide crystal. According to the present invention, the operation of the preparation method is convenient, and the crystallinity of the product is high; and the cerium oxide crystal prepared according to the preparation method is the chemical mechanical polishing liquid of grinding particles, and can provide excellent flattening polishing efficiency in the shallow ditch groove isolation polishing application.