The mechanical lidar based on time-of-flight principle uses the average value of short-time sequence multi pulse measurement as the target distance value, which will causes some virtual points in the point cloud data between targets. In order to filter the virtual point, the relationship between the depth of the virtual point and the distance between the adjacent points is analyzed, and the lightweight recognition formula of the virtual point is proposed. The experiment is completed on the SICK tim561 lidar. Experimental results show that the proposed method can effectively remove virtual points and improve the quality of point cloud.