A dynamic spectrum allocation method and device are provided. The method includes: finding non-idle frequency bands in the coverage of a communication device according to information in a database; selecting a frequency band from the non-idle frequency bands as a negotiation frequency band, and sending a spectrum assignment request to an interfering device using the negotiation frequency band; and acquiring usage assignment of the interfering device, in which the usage assignment is a response to the spectrum assignment request. The technical solutions can effectively allocate dynamic spectrum resources to a communication device, and are simple to implement.