Abstract：The algorithm of retrieving the horizontal visibility based on lidar was developed in this paper. The horizontal measurement data of lidar exists a linear area which is difficult to ascertain. The algorithm firstly iterates in special data segment to fix on the linear area,then expands the area to both ends,and finally gets the longest linear area. The horizontal extinction and visibility can be retrieved through the final linear area. The results compared with Vaisala apparatus indicate that the iterative expanding algorithm could be used to retrieve the horizontal visibility.