The present invention provides a method and an apparatus for sending a system information block in active state in a wireless communication system. Every NpBCH-cycle superframes send a system information block for one time. The system information block is carried on a main broadcast channel (pBCH0) physical channel by controlling the channel medium access control (MAC) protocol. The system information block is stopped to be transmitted by signaling transmission. If multi-carrier mode is carried out in multiple carriers, the system information block is sent on each carrier, wherein the content of the system information block, except the carrier ID, the FLReservedInterlaces and the NumFLReservedSubband, is same for all carriers.