Abstract: When cellular networks are utilized to locate the position of mobile station, in order to degrade the disadvantageous influence of non-line-of-sight propagation of radio waves on location performance, an improved location algorithm is proposed in this paper. In this algorithm the time difference of arrival and time of arrival measurements are firstly smoothed and reconstructed, then a two step weighted least square algorithm is employed to estimate the position of MS. Simulation shows that the location performance is significantly improved in non-line-of-sight propagation environment.