The invention relates to a partial differential coding and decoding method for 24-dimensional Golay modulation, and relates to the field of coherent light communication. At a sending end, every 12 bits of data belong to a group; partial differential coding of the bit 0 to the bit 4 is carried out; the bit 5 to the bit 11 are kept same; therefore, 12-bit partial differential coded data is obtained;the coded data is multiplied by a matrix generated by Golay code coding, so that a 24-bit Golay code word is obtained; the Golay code word is converted into a 24-dimensional Golay vector; 24 continuous BPSK code elements are modulated; a modulated signal is loaded in light and output; at a receiving end, when carrier recovery has discrepancy, the obtained Golay vector is inverted; 12-bit decisiondata is recovered through maximum likelihood judgment; differential decoding of the bit 0 to the bit 4 is carried out; and thus, the original data is recovered. According to the partial differentialcoding and decoding method and system for 24-dimensional Golay modulation disclosed by the invention, by utilization of a high-dimensional modulated algebraic structure, differential coding and decoding of part bits influenced by a carrier recovery ambiguous solution can be carried out; influence of the ambiguous solution is eliminated; and error of received data is avoided.