Channel assignment is an important issue in high throughput multi-channel wireless networks. Previous works on channel assignment use a common control channel to negotiate data channels by exchanging RTS/CTS. However, those schemes require time synchronization, which are hard to achieve in wireless networks. Moreover, employing negotiation-based schemes increase the end-toend delay of channel assignment in multi-hop communications. We propose an asynchronous scheme for channel assignment based on clustering nodes into a hierarchy. Channels are allocated from top to bottom in a cluster-bycluster basis. Simulation results show that the proposed channel assignment scheme significantly outperform negotiation-based schemes in terms of packet collision, path delay, and overall throughput.