Embodiments of this application provide a resource allocation method, an apparatus, and a system, to reduce a waste of resources and improve resource utilization. In the method, after determining a BWP allocated to a terminal device, where the BWP includes a first BWP, and determining a first value, a network device sends first indication information to the terminal device, where the first indication information is used to indicate the first value. The terminal device determines the BWP allocated by the network device to the terminal device, where the BWP includes the first BWP, and receives the first indication information from the network device. Then, when the first value is used to indicate a resource block group RBG size corresponding to the first BWP, the RBG size corresponding to the first BWP is determined based on the first value. Alternatively, when the first value is used to determine a resource indication value RIV set corresponding to the first BWP, the RIV set corresponding to the first BWP is determined based on the first value.