The invention provides a combined source-channel variable length symbol-class reversible decoding method, aiming at the two problems in the communication coding field that the source coding using variable length coding causes the error pervasion and the decoding end directly using the combined source-channel variable length symbol-class decoding causes the high complexity due to the excessive codeword symbols. At the encoding end, the output code flow of the source coding is binary run-length coded, and then the run-length is entropy coded by adopting the reversible variable length code, ultimately the reversible variable length code flow of the source is obtained; and at the decoding end, decoding is carried out by adopting a combined source-channel variable length symbol-class reversible decoding algorithm. The number of the source code flow code word symbols is greatly reduced, and the decoding complexity is reduced. Simultaneously, the decoding end can not only decode in the positive direction, but also can decode in the reverse direction when the positive decoding is wrong, the error pervasion degree is greatly reduced, and the transmitting performance of the communication system is improved. The method is applicable to the image, video and other multimedia transmission systems.