A signal transmission method, a terminal and a network-side device. A first network-side device sends access configuration (AC) indication information to a terminal, the AC indication information being used for indicating to the terminal the currently available AC in an access configuration set (ACS). The terminal receives the access configuration set (ACS) and the access configuration (AC) indication information sent by the network-side device, and determines, according to the AC indication information, the currently available AC in the ACS.