Embodiments of this application provide a configuration information obtaining method and an apparatus, which may be applied to a scenario in which a terminal device obtains an RNTI. The terminal device may be in RRC inactive mode. The method may include: obtaining a cell identifier, and obtaining first configuration information based on the cell identifier, where there is a correspondence between the cell identifier and the first configuration information, and the first configuration information is used to configure an RNTI; and performing one or more of the following operations based on the first configuration information: receiving downlink control information, receiving downlink data, sending uplink control information, or sending uplink data.