Embodiments provide a positioning method, an assistant site, and a system, to improve positioning accuracy of a mobile terminal. The method according to the embodiments of the present invention includes: generating, by an assistant site, a downlink assisted positioning signal; and sending, by the assistant site, the downlink assisted positioning signal to a mobile terminal. The downlink assisted positioning signal can enable a base station to determine position information of the mobile terminal based on a measurement result obtained by the mobile terminal by measuring the downlink assisted positioning signal.