In order to improve the positioning accuracy of wireless sensor networks, we improve a twice grid scanning positioning algorithm based on the GridScan algorithm, and further improve the positioning accuracy by using the triangle centroid iteration localization algorithm (TCILA). Firstly, the nearest neighbor anchor node is found by comparing the signal strength of all the neighbor anchor nodes of the unknown node to the unknown node, and the nearest neighbor anchor node is used to scan the estimated area of the relocated unknown node two times. And then the PIT rule is used to further reduce the positioning area. Finally, the centroid of the centroid triangle is iteratively calculated to get the final location. Simulation results show that in the same network environment, the improved algorithm can significantly improve the average relative positioning accuracy in comparison with traditional algorithms.