APIT is an approximate point-in triangulation method. The traditional APIT localization algorithm determines where the node is an interior point firstly, and then the Grid- SCAN algorithm is adopted to estimate the coordinates of the unknown node. However, there are large misjudgment probability and severe redundancy error in this method. In this paper, an improved APIT localization algorithm is proposed, which not only limits the selection range of neighbor nodes but also adopts Point-SCAN algorithm to estimation the position. We add TDMA protocol and study the performance of the algorithm by changing the node density and communication range. Simulation results show that our algorithm has better location performance than the traditional APIT algorithm and Centroid algorithm. In addition, it shows that collision has an impact on the location accuracy of the localization algorithm.