A reference signal transmission method, wherein the method is performed by a sending device and comprises: generating a reference signal sequence; determining a first index set based on a frame number, n f, of a radio frame, wherein the first index set indicates at least a part of reference signals in the reference signal sequence; determining, according to the first index set, the at least a part of reference signals in the reference signal sequence; mapping the at least a part of reference signals to a resource position that corresponds to the radio frame and that is used to transmit the at least a part of reference signals; and sending the at least a part of reference signals at the resource position; the method being characterized in that the reference signal is a narrowband positioning reference signal; wherein the first index set meets the following formula: m ′ = m 0 ′ + 2 n f mod 64 mod 220 wherein m' is the first index set; and when the method is used in an NB-IoT system deployed in a guard band or independently deployed, m 0 ′ meets the following formula: m 01 = 0,1 m 0 ′ = m 01 + N RB max, DL − 1, wherein N RB max, DL indicates a maximum quantity of RBs supported by the system, and N RB max, DL = 110; and when the method is used in the NB-IoT system deployed in-band, m 0 ′ meets the following formula: m 01 = 0,1 m 0 ′ = m 01 + 2 n PRB ′ + N RB max, DL − n ̃, wherein n PRB ′ is used to determine an index of the RB occupied by the NPRS, and ñ is used to indicate that a quantity of RBs corresponding to an LTE system bandwidth is an odd number or an even number; when ñ = 1, it represents that the quantity of RBs corresponding to the LTE system bandwidth is an odd number, or when ñ = 0, it represents that the quantity of RBs corresponding to the LTE system bandwidth is an even number; and N RB max,DL represents the maximum quantity of RBs supported by the system, and N RB max,DL = 110. generating a reference signal sequence; determining a first index set based on a frame number, n f, of a radio frame, wherein the first index set indicates at least a part of reference signals in the reference signal sequence; determining, according to the first index set, the at least a part of reference signals in the reference signal sequence; mapping the at least a part of reference signals to a resource position that corresponds to the radio frame and that is used to transmit the at least a part of reference signals; and sending the at least a part of reference signals at the resource position; the method being characterized in that the reference signal is a narrowband positioning reference signal; wherein the first index set meets the following formula: m ′ = m 0 ′ + 2 n f mod 64 mod 220 wherein m' is the first index set; and when the method is used in an NB-IoT system deployed in a guard band or independently deployed, m 0 ′ meets the following formula: m 01 = 0,1 m 0 ′ = m 01 + N RB max, DL − 1, wherein N RB max, DL indicates a maximum quantity of RBs supported by the system, and N RB max, DL = 110; and when the method is used in the NB-IoT system deployed in-band, m 0 ′ meets the following formula: m 01 = 0,1 m 0 ′ = m 01 + 2 n PRB ′ + N RB max, DL − n ̃, wherein n PRB ′ is used to determine an index of the RB occupied by the NPRS, and ñ is used to indicate that a quantity of RBs corresponding to an LTE system bandwidth is an odd number or an even number; when ñ = 1, it represents that the quantity of RBs corresponding to the LTE system bandwidth is an odd number, or when ñ = 0, it represents that the quantity of RBs corresponding to the LTE system bandwidth is an even number; and N RB max,DL represents the maximum quantity of RBs supported by the system, and N RB max,DL = 110.