Abstract: Because of the atmospheric disturbance and the detector noise, lidar echo signal usually contains a lot of random noise. It is important to smooth the lidar signal before retrieving the atmospheric parameters. A iteration method base on half-step interpolation(HSI) is introduced in the paper. Using the raw data as the original signals, the proposed method could reconstruct the new data by repeating the HSI process until the similarity of adjacent iterated results being smaller than a setting criterion. One of the advantages of the new method is that the data segmentation processing could be omitted. Experiments show that the algorithm can effectively improve the smoothness of the lidar echo and can save the important signal fluctuation adaptively.