How to obtain location information of an unknown node precisely is a key problem of locating service under ubiquitous computing environment.The paper proposes and proves three theorems of location reference nodes placement according to the analysis of the location error produced during location using the polygon location method and the three important characteristics of Chaos Dynamics.Based on the three theorems

the location reference nodes selection algorithm (LRNS algorithm) is proposed by improving the traditional polygon location algorithm.The simulation results indicate that the reference nodes placement theorems and the LRNS algorithm can meet the requirements of ubiquitous terminals'real-time location and possesses the preferable location precision.