A method for making a prism sheet includes: providing a cutting device comprising a cutter, a table plate, and a control unit, the table plate controlled to move up and down by the control unit, and the cutter having a blade rotatable; providing a mold insert preform on the table plate, the mold insert preform having a flat surface; moving the cutter to etch the flat surface of the mold insert preform along a first direction, and simultaneously driving the table plate to move up and down by the control unit in a first predetermined manner to form first elongated depressions in the flat surface; moving the cutter to etch the flat surface of the mold insert preform along a second direction to form second elongated depressions in the flat surface, thereby forming a mold insert; using the mold insert to form the prism sheet by injection molding method.