This application provides a downlink control information transmission method, an apparatus, and a system. The method includes: sending, by a gNB, downlink control information (DCI) to UE on a first bandwidth resource, where the DCI is used for data transmission between the gNB and the UE on the first bandwidth resource or data transmission between the gNB and the UE on a second bandwidth resource; and if the DCI is used for data transmission between the gNB and the UE on the first bandwidth resource, a size of the DCI is L1_1, or if the DCI is used for data transmission between the gNB and the UE on the second bandwidth resource, a size of the DCI is L1_2, where L1_1 is equal to L1_2, and L1_1 and L1_2 are integers greater than or equal to 1.