A method and apparatus for beam detection in a wireless communication system. In one embodiment, the method includes the UE initiating a RA procedure. The method also includes the UE transmitting multiple RA preambles to a base station of the cell at different occasions for the base station to determine a beam set of the UE. The method further includes the UE starts monitoring a PDCCH for RA response reception from the base station after finishing transmissions of the multiple RA preambles.