A method and an apparatus for positioning a terminal device. The method includes: generating, by a terminal device, a first message, where the first message includes one or more pieces of first time difference information, and the first time difference information includes a first time difference and information about a first positioning reference signal pair corresponding to the first time difference, where the first positioning reference signal pair includes a first uplink positioning reference signal and a first downlink positioning reference signal that have an association relationship, and the first time difference is a time difference between a sending time point of the first uplink positioning reference signal and a receiving time point of the first downlink positioning reference signal; and sending, by the terminal device, the first message to a network device.