In this paper, firstly, the number of positions for beacon is deduced to send a signal according to the acreage of ROI (region of interest); then a simple method is presented to calculate the coordinates of the sending positions in rectangular ROI; and then, a method is advanced based on virtual force to arrange the positions in arbitrary ROI; further, the wandering salesman problem (WSP) algorithm is applied to the positions sequence so as to get the optimal path touring it. When mobile beacon moves according to the optimal path and emits RF signals at every position, the sensors in ROI could work out their position with multilateration. Experimental results demonstrate that the proposed localization method is efficient and flexible.