This application relates to the field of communications technologies, and discloses a DMRS port determining method and a communications apparatus, to resolve a problem that collisions occur on DMRS ports used by a large quantity of terminal devices to send uplink data and a random access effect is affected during 2-step random access. The method includes: receiving, by a terminal device, configuration information sent by a network device, where the configuration information includes DMRS configuration information and indication information of a DMRS port set, the DMRS configuration information is used to configure a plurality of DMRS ports, and the indication information of the DMRS port set is used to indicate one or more available DMRS ports in the plurality of DMRS ports; and determining, by the terminal device, a target DMRS port in the DMRS port set.