The present disclosure relates to SFN indication methods, terminal devices, and positioning servers and systems. One example method includes obtaining an SFN offset indication parameter of a cell i, sending the SFN offset indication parameter of the cell i to a terminal device, receiving the SFN offset indication parameter of the cell i from the positioning server, obtaining a frame number of a radio frame n of a cell j, and determining a phase rotation parameter of the cell i based on the frame number of the radio frame n of the cell j and the SFN offset indication parameter of the cell i, or obtaining a sequence initialization factor used by a narrowband positioning reference signal (NPRS) on a 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.