A method for selecting a serving cell by a user equipment (UE) to which the inter-site carrier aggregation (CA) technology is according to the intensity of a reception signal of each carrier wave is provided. However, in order to improve resource usage and a throughput of the entire cells, a method is performed in which a PCell and an SCell are selected considering the intensity of a reception signal and a load between cells, the SCell is activated, and loads of the PCell and the SCell are adjusted. The method can balance an inter-cell traffic load, and eventually, increase usage of the entirety of a network and improve a throughput.