The localization algorithm in wireless sensor network is always a hot spot. Information collected by the sensors is meaningless without the position of the sensors. Now, paying little attention to 3-D space, most of the algorithms are for 2-D space. In this paper we introduce a novel algorithm for 3-D space called OBS (Optimal Beacon Selection) algorithm. In this algorithm we launched the concept of position error parameter, with consideration of communication range and position accuracy of beacon. The experiment results show that this method can minimize the accumulation error and improve the location precision.