Abstract: Elevating the capability of simultaneous transmitting is one of the key issues in VANETs studies. If equipped with multiple wireless interfaces, each vehicle can simultaneously transmit over different channels, which has positive impact on the extension of communication window and the promotion of network throughput. Challenging research issues in multi-interface vehicular ad hoc networks are the spectrum allocation and the routing problems. Considering that the negative effects of the topological dynamic on spectrum allocation in VANETs, an algorithm of spectrum allocation based on clustering is presented, which could be utilized in multi-interface VANETs. Firstly, the network is clustered according to the velocity of vehicles. And then an off-line spectrum allocation scheme is applied to the inter-cluster links, thus eliminating the impact of the topological dynamic. Considering that the velocities of the vehicles from same cluster are similar, the topology of intra-cluster is stable. It is helpful to the application of dynamic spectrum allocation technology. Simulation results demonstrate that our method can effectively promote network throughput and perform well on dynamic topology.