A reference signal transmission method, comprising: receiving, by a first communications device, radio resource control, RRC signaling, first configuration information about a reference signal, and second configuration information about a part bandwidth, BWP, wherein the first configuration information indicates a first initial resource index and a first configured bandwidth of the reference signal, the second configuration information indicates a second initial resource index and a second configured bandwidth of the BWP, and the first initial resource index is a common resource block, CRB, index, the second initial resource index is a CRB index, wherein the first configured bandwidth is multiples of 4 RBs, and the second configured bandwidth is multiples of 1 RB; determining, by the first communications device, a first frequency band based on the first initial resource index, the second initial resource index, the first configured bandwidth, and the second configured bandwidth, wherein the first initial resource index is greater than or equal to the second initial resource index, and the first initial resource index is less than or equal to a sum of the second initial resource index and the second configured bandwidth; and receiving, by the first communications device, the reference signal on the first frequency band, wherein if a sum of the first initial resource index and the first configured bandwidth is greater than or equal to the sum of the second initial resource index and the second configured bandwidth, the first frequency band meets the following condition: a bandwidth of the first frequency band = the second initial resource index + the second configured bandwidth - the first initial resource index. receiving, by a first communications device, radio resource control, RRC signaling, first configuration information about a reference signal, and second configuration information about a part bandwidth, BWP, wherein the first configuration information indicates a first initial resource index and a first configured bandwidth of the reference signal, the second configuration information indicates a second initial resource index and a second configured bandwidth of the BWP, and the first initial resource index is a common resource block, CRB, index, the second initial resource index is a CRB index, wherein the first configured bandwidth is multiples of 4 RBs, and the second configured bandwidth is multiples of 1 RB; determining, by the first communications device, a first frequency band based on the first initial resource index, the second initial resource index, the first configured bandwidth, and the second configured bandwidth, wherein the first initial resource index is greater than or equal to the second initial resource index, and the first initial resource index is less than or equal to a sum of the second initial resource index and the second configured bandwidth; and receiving, by the first communications device, the reference signal on the first frequency band, wherein if a sum of the first initial resource index and the first configured bandwidth is greater than or equal to the sum of the second initial resource index and the second configured bandwidth, the first frequency band meets the following condition: a bandwidth of the first frequency band = the second initial resource index + the second configured bandwidth - the first initial resource index.