To estimate the distance and localization in the wireless sensor networks (WSN), the RSSI (Received Signal Strength Indicator) value is generally assumed to have a linear relationship with the logarithm of distance communication. This is true in the absence of obstacles and wireless interference, as is the case in the free space. In this paper, the principle of nodes localization in wireless sensor networks is analyzed on the basis of RSSI as metric for estimating distances in outdoor environment. The measure of nodes distances and localization process are described. CC2530 RF module is used as a hardware platform of nodes on the location experiment. The results of localization algorithms (Trilateration and Multilateration) in Wireless Sensor Networks are presented. Test results show that the mean errors are around 4.9 m in a real-world environment for the Trilateration algorithm and around 0.5 m for Multilateration algorithm.