A method for transmitting a Broadcast Channel Assignment Message, BCAM, in a trunking system characterized by, comprising: constructing, by a base station side, a BCAM without resources after channel resource of a conventional group call is successfully established, generating a hash time slot list according to an acquired International Mobile Subscriber Identity, IMSI, list, determining a paging time slot monitored by a called terminal according to the hash time slot list, and placing the BCAM without resources to a queue corresponding to the paging time slot monitored by the called terminal; transmitting, by the base station side, the BCAM without resources in the queue to the called terminal, which enters a non-time-slot monitoring mode after demodulating the BCAM without resources; and constructing, by the base station side, a BCAM with resources, and transmitting the BCAM with resources to the called terminal in a last paging time slot in a time slot period; wherein the placing the BCAM without resources to a queue corresponding to the paging time slot monitored by the called terminal comprises: when there are a called terminal supporting a positive time slot period index and a called terminal supporting a negative time slot period index in the conventional group, calculating the time slot period based on the negative time slot period index, placing the BCAM without resources to a paging time slot monitored by the called terminal supporting the negative time slot period index in a first time slot period according to the hash time slot list, and placing the BCAM without resources to a paging time slot monitored by the called terminal supporting the positive time slot period index in a second time slot period according to the hash time slot list; wherein the positive time slot period index is equal to the absolute value of the negative time slot period index, the first time slot period is a time slot period starting from a current paging time slot, and the second time slot period is a time slot period following a last paging time slot in the first time slot period. constructing, by a base station side, a BCAM without resources after channel resource of a conventional group call is successfully established, generating a hash time slot list according to an acquired International Mobile Subscriber Identity, IMSI, list, determining a paging time slot monitored by a called terminal according to the hash time slot list, and placing the BCAM without resources to a queue corresponding to the paging time slot monitored by the called terminal; transmitting, by the base station side, the BCAM without resources in the queue to the called terminal, which enters a non-time-slot monitoring mode after demodulating the BCAM without resources; and constructing, by the base station side, a BCAM with resources, and transmitting the BCAM with resources to the called terminal in a last paging time slot in a time slot period; when there are a called terminal supporting a positive time slot period index and a called terminal supporting a negative time slot period index in the conventional group, calculating the time slot period based on the negative time slot period index, placing the BCAM without resources to a paging time slot monitored by the called terminal supporting the negative time slot period index in a first time slot period according to the hash time slot list, and placing the BCAM without resources to a paging time slot monitored by the called terminal supporting the positive time slot period index in a second time slot period according to the hash time slot list; wherein the positive time slot period index is equal to the absolute value of the negative time slot period index, the first time slot period is a time slot period starting from a current paging time slot, and the second time slot period is a time slot period following a last paging time slot in the first time slot period.