Embodiments of this application disclose a resource allocation method and a related device and system. The method may include: allocating a resource group including M first resource blocks to a terminal when allocating uplink resources, where an occupancy ratio of a frequency spacing formed by the M first resource blocks to a system bandwidth is greater than a preset threshold, and the resource group further includes N second resource blocks in any frequency domain positions, where M≥2, N≥1, and both M and N are positive integers; and sending resource indication information to the terminal, where the resource indication information includes information about the resource group. According to the embodiments of this application, scheduling of uplink resources can be more flexible for use of an unlicensed frequency band while the OCB requirement of ETSI is met.