A carrier assignment method, a multi-carrier base station and a wireless communication device using the same are proposed. The carrier assignment method is adapted for assigning carriers in a paging group for an ABS with multi-carriers, and includes the following step. At least two paging carriers is assigned in a paging group, where all assigned carriers belonging to a paging group are in the same frequency band. Also, small but close frequency bands are grouped into a super band, where different carriers in different super bands are assigned into different paging groups. The wireless communication device determines the paging carrier index for itself by a mapping function of a mobile identification and the number of carriers. The paging message for the wireless communication device is sent only on the paging carrier corresponding to the determined paging carrier index.