A system frame number, SFN, indication method, comprising: obtaining, by a positioning server, an SFN initialization moment of the cell i from the cell i, and an SFN initialization moment of the cell j from the cell j; generating, by the positioning server, an SFN offset indication parameter of the cell i based on the SFN initialization moment of the cell i and the SFN initialization moment of the cell j, by using the following formula: SFN _ offset i = ⌊ t j − t i T ⌋ mod N, where the SFN _ offset i is the SFN offset indication parameter of the cell i; the t j is the SFN initialization moment of the cell j that is reported by the cell j; the t i is the SFN initialization moment of the cell i that is reported by the cell i; the T is the time length of the radio frame; the N is a positive integer and indicates a maximum indication range of the SFN offset indication parameter; the └ ┘ is a rounding down operation; and sending, by the positioning server, the SFN offset indication parameter to the terminal device through the cell j by using an LTE Positioning Protocol A,LPPa, message; obtaining, by the terminal device, a frame number SFN j of the radio frame n of the cell j; determining, by the terminal device, a phase rotation parameter of the cell i used for detecting a narrowband secondary synchronization signal, NSSS, sequence, based on the frame number SFN j of the radio frame n of the cell j and the SFN offset indication parameter of the cell i that is received by the terminal device; or obtaining, by the terminal device, based on the frame number SFN j of the radio frame n of the cell j and the SFN offset indication parameter of the cell i, a sequence initialization factor c init used by a narrowband positioning reference signal NPRS on the radio frame m of the cell i, and obtaining the NPRS on the radio frame m of the cell i based on the sequence initialization factor c init of the cell i. obtaining, by a positioning server, an SFN initialization moment of the cell i from the cell i, and an SFN initialization moment of the cell j from the cell j; generating, by the positioning server, an SFN offset indication parameter of the cell i based on the SFN initialization moment of the cell i and the SFN initialization moment of the cell j, by using the following formula: SFN _ offset i = ⌊ t j − t i T ⌋ mod N, where the SFN _ offset i is the SFN offset indication parameter of the cell i; the t j is the SFN initialization moment of the cell j that is reported by the cell j; the t i is the SFN initialization moment of the cell i that is reported by the cell i; the T is the time length of the radio frame; the N is a positive integer and indicates a maximum indication range of the SFN offset indication parameter; the └ ┘ is a rounding down operation; and sending, by the positioning server, the SFN offset indication parameter to the terminal device through the cell j by using an LTE Positioning Protocol A,LPPa, message; obtaining, by the terminal device, a frame number SFN j of the radio frame n of the cell j; determining, by the terminal device, a phase rotation parameter of the cell i used for detecting a narrowband secondary synchronization signal, NSSS, sequence, based on the frame number SFN j of the radio frame n of the cell j and the SFN offset indication parameter of the cell i that is received by the terminal device; or obtaining, by the terminal device, based on the frame number SFN j of the radio frame n of the cell j and the SFN offset indication parameter of the cell i, a sequence initialization factor c init used by a narrowband positioning reference signal NPRS on the radio frame m of the cell i, and obtaining the NPRS on the radio frame m of the cell i based on the sequence initialization factor c init of the cell i.