The localization system based on received signal strength indication (RSSI) is vulnerable to environmental impact, we therefore present a RSSI signal processing optimization strategy based on clustering analysis of the Gaussian mixture model. We achieve accurate indoor localization of unknown nodes through the optimization of the RSSI and the distance rectification of the four sides centroid localization algorithm. Experiments on Bluetooth 4.0 beacon nodes validate that the algorithm can effectively improve range accuracy and location precision. The location precision is increased by 34.6% than the conventional weighted centroid algorithm, and the average error of localization is less than 0.5 m, which  meets the location precision requirement.