This application relates to the field of wireless communications, and in particular, to a communication method, an apparatus, and a system in a wireless communications system. In the method, a terminal device detects a physical downlink control channel PDCCH sent by a network device, the PDCCH carries indication information, and the indication information is used to indicate a type of system information; the terminal device determines, based on the indication information, a physical resource carrying the system information; and the terminal device receives the system information on the physical resource. Based on this method, a network device can flexibly indicate a type of system information that needs to be sent.