Circular sensing field is considered in this paper, a range-free localization scheme is proposed for wireless sensor networks (WSNs) by using four beacon nodes (BNs) equipped with a directional antenna. Each beacon node rotates at a constant angular speed and broadcasts its angular bearings and its coordinate. A sensor node can compute its location by sine theorem through receiving the angular bearings and the coordinates from the four xed beacon nodes. The proposed method is of lower computation complexity and without increasing the hardware cost of the sensor nodes based on an angle-of-arrival estimation technique. The mean localization error of the sensor nodes is the least when the four beacon nodes locate at the Sqrt(2)/2 radius of sensing field location range from the center of the sensing field. Error analysis and computer simulation show that the errors of the sensor node’s x-coordinate and y-coordinate increase with the increase of the square of the distance from origin and the product of angular speed and beacon distance. The algorithm shows the characteristics of high accuracy, robust and that the error is controllable.