Aiming at the problem of three dimensional（ 3D） localization of mobile terminals in indoor non-line-ofsight（ NLOS） wireless environment

an improved 3 D positioning model based on the least square method in nonline-of-sight environment is proposed. Firstly

the linear relationship between the true value of the wireless signal time of arrival（ TOA） and the measured value can be found. Then

according to the linear relationship

the mobile terminal is positioned in 3D by using the least squares. Next

the data model for the target of positioning optimization is set

and the high-precision positioning of the terminal equipment is completed with as few base stations as possible. The experimental results show that the maximum positioning error of the model in NLOS environment is not more than 1. 5 m

the positioning precision is significantly improved and prior to other positioning models.