According the characteristic of wireless sensor net works (WSN), it can be used in warehouse monitoring. However, there are problems in localiza tion. Existing RSSI-based approaches rely on absolute RSSI values to estimate physical distances . However, RSSI has a lager variation because its fading, shadowing and reflections. By comparing RSSI values of the mobile beacon, we propose an improved RSSI-based approach which can achieve higher accuracy. In this paper, RSSI localization is introduced firstly. Second, we propose a localizati on algorithm based on the comparison of the mobile beacon node's RSSI. Third, we analyze the algorithm with simulation experiment. Finally, we draw conclusion