A frequency allocation method and device for an unauthorized frequency band. The method includes: a controller acquires a business load status of plural macro base stations having similar coverage ranges and operated by different operators, and generates, based on the business load status, allocation information about an unauthorized frequency band, to mutually exclusively allocate the unauthorized frequency band to plural macro base stations; the macro base stations receive the allocation information about the unauthorized frequency band, to determine the unauthorized frequency band monopolized by the macro base stations from an unauthorized frequency band resource, and generate indicative information about the monopolized unauthorized frequency band; and a small base station receives the indicative information, detects state of the unauthorized frequency band monopolized by the macro base stations, and dynamically accesses, according to a detecting result, a specific unauthorized frequency baud in the unauthorized frequency band monopolized by the macro base stations.