A method for transmitting system information by an access network device, comprising: generating a system information block SIB, wherein generating the SIB comprises encoding and rate matching a source SIB and storing the encoded SIB in a ring buffer, the encoded SIB comprises an information bit stream and two check bit streams, the rate matching comprises interleaving each bit stream in the encoded SIB, to obtain three data matrices of equal size, and storing the encoded SIB in the ring buffer comprises sequentially storing the three data matrices in the ring buffer; and periodically sending the SIB in N time units in one SIB period, wherein the SIB period comprises T time unit groups of which T P are candidate SIB sending time unit groups, the periodically sending the SIB comprising, for each candidate SIB sending time unit group: performing a clear channel assessment CCA; and if the CCA succeeds, sending the SIB in r candidate SIB sending time units in the candidate SIB sending time unit group, wherein: the access network device determines a redundancy version number corresponding to the SIB sent in each of the r candidate SIB sending time units, the redundancy version number indicating a start point in the ring buffer from which the SIB is read, wherein different redundancy version numbers indicate different start points, compared with information bits included in the SIB corresponding to other redundancy version numbers, there is a quantity of information bits included in the SIB corresponding to the redundancy version number 0, and a redundancy version number of the SIB sent in a first time unit of the N time units is 0. generating a system information block SIB, wherein generating the SIB comprises encoding and rate matching a source SIB and storing the encoded SIB in a ring buffer, the encoded SIB comprises an information bit stream and two check bit streams, the rate matching comprises interleaving each bit stream in the encoded SIB, to obtain three data matrices of equal size, and storing the encoded SIB in the ring buffer comprises sequentially storing the three data matrices in the ring buffer; and periodically sending the SIB in N time units in one SIB period, wherein the SIB period comprises T time unit groups of which T P are candidate SIB sending time unit groups, the periodically sending the SIB comprising, for each candidate SIB sending time unit group: performing a clear channel assessment CCA; and if the CCA succeeds, sending the SIB in r candidate SIB sending time units in the candidate SIB sending time unit group, wherein: the access network device determines a redundancy version number corresponding to the SIB sent in each of the r candidate SIB sending time units, the redundancy version number indicating a start point in the ring buffer from which the SIB is read, wherein different redundancy version numbers indicate different start points, compared with information bits included in the SIB corresponding to other redundancy version numbers, there is a quantity of information bits included in the SIB corresponding to the redundancy version number 0, and a redundancy version number of the SIB sent in a first time unit of the N time units is 0. performing a clear channel assessment CCA; and if the CCA succeeds, sending the SIB in r candidate SIB sending time units in the candidate SIB sending time unit group, wherein: the access network device determines a redundancy version number corresponding to the SIB sent in each of the r candidate SIB sending time units, the redundancy version number indicating a start point in the ring buffer from which the SIB is read, wherein different redundancy version numbers indicate different start points, compared with information bits included in the SIB corresponding to other redundancy version numbers, there is a quantity of information bits included in the SIB corresponding to the redundancy version number 0, and a redundancy version number of the SIB sent in a first time unit of the N time units is 0. the access network device determines a redundancy version number corresponding to the SIB sent in each of the r candidate SIB sending time units, the redundancy version number indicating a start point in the ring buffer from which the SIB is read, wherein different redundancy version numbers indicate different start points, compared with information bits included in the SIB corresponding to other redundancy version numbers, there is a quantity of information bits included in the SIB corresponding to the redundancy version number 0, and a redundancy version number of the SIB sent in a first time unit of the N time units is 0.