A method of designing a look-up table of a finite-state encoder, applied to a finite-state encoder, comprises steps of: determining a bit length of a legal output codeword derived from the finite-state encoder and a restrict condition; collecting a plurality of legal output codeword satisfied the restrict condition; determining a bit length of an input codeword derived to the finite-state encoder according to the amount of the plurality of the legal output codeword; determining the amount of states in the finite-state encoder according to the bit length of the input codeword and the bit length of the legal output codeword; dividing the plurality of legal output codeword to a plurality of subset according to the amount of the states in the finite-state encoder and a specific mathematic equation; determining the amount of the legal output codewords in the plurality of subset; and, completing the look-up table through determining a relationship among a present state, a previous state, and a corresponding subset, wherein the amount of the subsets used in the look-up table is greater than the amount of the states in the finite-state encoder and smaller than two times of the amount of the states in the finite-state encoder.