The invention discloses a clustering method for the in-vehicle Ad hoc network based on the signal strength, and provides a network clustering and maintaining method which starts with the vehicle directional information, and enables the vehicles running along the same direction to participate in the process that the same cluster is formed and maintained. After a node is initialized, tentative cluster-heads are established among the vehicles running along the same direction, neighbor linked lists are formed in the two-hop range of the tentative cluster-heads, the node which has the maximum nodal connection signal strength is a cluster-head node, and other nodes are common nodes or gateway nodes of the cluster; the maintenance process is based on the vehicle directional information and the nodal connection signal strength. As considering the vehicle directional information and the nodal connection strength signal, the invention has the advantages that the in-vehicle Ad hoc network clustering structure is stable by comparing with other methods under the urban traffic environment, the node alternating times and the clustering related control information quantity are less, the problem that the in-vehicle Ad hoc network performance is low under the urban traffic environment is solved, the cluster service life is prolonged, and the network state is improved.