A method and apparatus of user equipment (UE) in a wireless communication system supporting a shared spectrum channel access is provided. The method and apparatus comprises: receiving, from a base station (BS), a physical downlink control channel (PDCCH) including downlink control information (DCI); determining, based on the received DCI, time domain resource allocation information of a random access channel (RACH) occasion and channel sensing information; performing channel sensing on an uplink (UL) channel based on the determined channel sensing information; identifying a status of the UL channel based on a result of the channel sensing on the UL channel; and transmitting, to the BS, a physical random access channel (PRACH) preamble over the UL channel based on the determined time domain resource allocation information and the identified status of the UL channel.