Embodiments of this application provide a method, the method includes: sending, by the RRC entity, a first RRC message to a lower-layer entity, and receiving, by the MAC entity, a first RRC message from an upper-layer entity, where the first RRC message includes to-be-transmitted data; determining, by the MAC entity, a first random access preamble if a data amount supported by a coverage level of the communications apparatus meets a size of the first RRC message, where the first random access preamble is used to indicate that the first RRC message is to be sent in a random access process.