Abstract: A range-free localization algorithm using mobile nodes for wireless sensor network(WSN) is proposed.In this algorithm,a mobile node travels across the communication range of the unknown node in two vertical paths,and gets some beacon localizations near the border of communication range.A geometric constraint area is formed by the perpendicular bisector of the segments connecting beacon points.The center of the area is the estimated location of the unknown node. Comparing with other methods based on geometric constraint,the proposed method provides lower computation complexity and higher localization accuracy.Simulation experiment results show that the proposed method outperforms other methods by 10% to 40% in localization accuracy.