load in the system is selected and the source enb 10 is notified of the component carrier cc 2 with the lowest traffic load in the system and its traffic load related information or the source enb 10 is notified of both of the component carriers cc 2 and cc 3 and their traffic load related information wherein both the component carriers cc 2 and cc 3 have traffic loads lower than that of the component carrier cc 1 in this embodiment next after the source enb 10 receives the information of the component carriers cc 2 and cc 3 with lower traffic loads from the destination enb 20 the source enb 10 then determines a primary component carrier synthetically considering the measurement information from the user equipment 30 reflecting a channel quality etc for example the cc 2 with the lowest traffic load and a better channel quality is selected as the primary component carrier and the destination enb 20 is notified of that the component carrier cc 2 is determined the primary component carrier those skilled in the art shall appreciate here that while the process of determining the primary component carrier is completed after only one interactive coordination between the source enb 10 and the destination enb 20 in the foregoing embodiments of the invention when the destination enb 20 is notified of the primary component carrier e g the cc 2 determined by the source enb 10 after synthetically considering the measurement information of the component carriers from the user equipment and the traffic loads.