Embodiments of the present invention relate to the field of communications technologies and provide a method for transmitting system information, an apparatus, and a system, to reduce a delay in obtaining correct system information by a terminal device. One method includes: generating a system information block SIB, and sending the SIB in N time units of a SIB period, wherein a first time unit of the N time units includes a redundancy version number of the SIB that is set to 0, the SIB period comprises T time unit groups, and the T time unit groups comprise TP SIB candidate sending time unit groups, wherein TP≤T, each of the T time unit groups comprises A time units for a clear channel assessment (CCA), and each of the TP SIB candidate sending time unit groups comprises r SIB candidate sending time units, and wherein N is a total quantity of SIB candidate sending time units comprised in one or more of the TP SIB candidate sending time unit groups that the CCA is successful, and N≤TP×r.