A method and a server for determining a location of a targeted mobile set using Secure User Plane Location (SUPL) in a wireless communications network are provided. The method includes receiving a request message requesting location information of the targeted mobile set, from a SUPL agent; sending a location initiation message (SUPL INIT) to the targeted mobile set in response to the received request message from the SUPL agent; determining a positioning method for the location service of the targeted mobile set after receiving a location capability from the targeted mobile set; and performing each of a plurality of positioning procedures by using the determined positioning method until a timer related to the determined positioning method is due or the target mobile set obtains a new positioning method, wherein the plurality of the positioning procedures are performed when an event of the targeted mobile set occurs or when triggered periodically.