In recent years, positioning systems are widely used in many parts of daily life, such as travel, field exploration, mountain rescue and so on. There are two main outdoor positioning technologies, namely a global positioning system (GPS) and a received signal strength indicator (RSSI). Since the GPS, which is depending on a good satellite signal environment, is generally used in the outside where has little building and trees, the RSSI has gradually become popular in recent years for mountain rescue. The advantage of RSSI is that all systems based on wireless communication can use the RSSI-based positioning methods as long as these systems can measure the RSSI. These positioning methods all estimate the coordination of the positioning target by converting the RSSI into distance and combining the distance with the position of the signal receiver. However, the noise of the surrounding environment will cause errors in the RSSI and affect the positioning results. Therefore, a pre-processing method to reduce the influence of noise to a certain extent is considered necessary. In this paper, a method for raw RSSI data pre-processing is proposed. The effeteness of the method is confirmed through a simulation and several experiments.