Methods and apparatus are provided for a UE to determine a UL spatial relation for an UL transmission in response to an unknown UL spatial relation switch. The UE may determine whether the UL spatial relation is based on an SRS transmission in UL, a CSI-RS in DL, or an SSB in the DL. If the UL spatial relation is based on the SRS transmission, the UE may select the UL spatial relation for the UL transmission corresponding to a Tx beam of the SRS transmission. If the UL spatial relation is based on the CSI-RS or the SSB, the UE may select the UL spatial relation for the UL transmission based on whether the unknown UL spatial relation switch s due to a corresponding resource for beam training not being configured by a communication network or a corresponding beam information being expired.