A beam determining method performed in an uplink random access procedure, a user equipment, and a base station are disclosed. The user equipment has a plurality of RX beams, the base station has a plurality of TX beams. A beam determining method performed by a user equipment includes: determining an available RX beam among the plurality of RX beams of the user equipment and an available TX beam among the plurality of TX beams of the base station according to downlink synchronization signals transmitted by the base station; notifying the base station of information indicating the available TX beam of the base station implicitly.