A lookup table generation method, comprising: dividing a first symbol sequence into two symbol sub-sequences, wherein symbols that are from the first symbol to a center symbol in the first symbol sequence form one symbol sub-sequence, and symbols that are from the center symbol to the last symbol in the first symbol sequence form the other symbol sub-sequence; the first symbol sequence is any symbol sequence in a preset group of N symbol sequences of a length of N symbols each; when N is an odd number, the center symbol is the (N+1)/2 th symbol in the first symbol sequence, and when N is an even number, the center symbol is the N/2 th symbol or the N/2+1 th symbol in the first symbol sequence; and N is an integer not less than 3; performing statistical averaging on each symbol sub-sequence, and calculating a corresponding non-linear deviation value according to a result of the statistical averaging; correspondingly storing the symbol sub-sequence in which the center symbol is the last symbol and the corresponding non-linear deviation value of the symbol sub-sequence to form a first lookup table in a cascaded lookup table; and correspondingly storing the symbol sub-sequence in which the center symbol is the first symbol and the corresponding non-linear deviation value of the symbol sub-sequence to form a second lookup table in the cascaded lookup table, wherein when N is greater than 3, the method further comprises: reducing a quantity of levels in possible levels of each of one or more edge symbols except a highest level and a lowest level, wherein the one or more edge symbols are symbols in the first symbol sequence or the symbol sub-sequences except the center symbol and a symbol adjacent to the center symbol. dividing a first symbol sequence into two symbol sub-sequences, wherein symbols that are from the first symbol to a center symbol in the first symbol sequence form one symbol sub-sequence, and symbols that are from the center symbol to the last symbol in the first symbol sequence form the other symbol sub-sequence; the first symbol sequence is any symbol sequence in a preset group of N symbol sequences of a length of N symbols each; when N is an odd number, the center symbol is the (N+1)/2 th symbol in the first symbol sequence, and when N is an even number, the center symbol is the N/2 th symbol or the N/2+1 th symbol in the first symbol sequence; and N is an integer not less than 3; performing statistical averaging on each symbol sub-sequence, and calculating a corresponding non-linear deviation value according to a result of the statistical averaging; correspondingly storing the symbol sub-sequence in which the center symbol is the last symbol and the corresponding non-linear deviation value of the symbol sub-sequence to form a first lookup table in a cascaded lookup table; and correspondingly storing the symbol sub-sequence in which the center symbol is the first symbol and the corresponding non-linear deviation value of the symbol sub-sequence to form a second lookup table in the cascaded lookup table, wherein when N is greater than 3, the method further comprises: reducing a quantity of levels in possible levels of each of one or more edge symbols except a highest level and a lowest level, wherein the one or more edge symbols are symbols in the first symbol sequence or the symbol sub-sequences except the center symbol and a symbol adjacent to the center symbol.