A decompression method for communication network is provided, in which such fields as an SN are compressed by using an ROHC scheme. The ROHC uses a WLSB algorithm to compress some fields which change regularly, and decodes by using the decompressor's context through transmitting the low significant bits in these fields. In order to avoid using the inefficient ergodic method and the incorrect direct replacing method in low bits, based on the mathematical characteristics of the definition of interpretation intervals, decoding is performed such that the low bits is determined by the received k significant bits while the high bits is determined jointly by the local storage information and these k significant bits. Its decoding method can be used for decompression of an SN, a TS and an IP-ID in an ROHC compression.