A method of building a locating service for a wireless network environment includes: an environment input step, a detection point calculation step, a measuring step and an assumed non-detected position point step to find measured position points and to measure a four-directional signal strength of the measured position point. By assuming signal strengths of non-detected position points, an entire positioning system can be established. A measuring process includes a portable device signal measuring step, a position point calculation step, and a signal feed back step to send the corresponding position information to the portable device to provide information to a user.