This paper proposes a method for the IP layer link aggregation using flow information to use all available mobile interfaces for backbone network access simultaneously in a vehicle mobile router. For this purpose, we present the design of the IP layer link aggregation functionality and the design of the aggregator which is the essential part of the IP layer link aggregation functionality. In the proposed method, the traffic distributor transmits the packets in the same session to only one mobile interface and uses the flow information as an identifier to distinguish each session.