Aiming at the difficulty of filtering the clustered and isolated data far away from the main point cloud caused by occlusion in the linear measurement data of LiDAR, a point cloud filtering method combined with digital signal processing technology was proposed. The height difference sequence is constructed for the adjacent points in the data section, the discrete Fourier transform was used to solve the amplitude frequency response of the height difference sequence. After low-pass filtering and inverse Fourier transform of frequency domain signal, the comparison signal with greatly modified isolated data was restored. By comparison signal ,we cloud find the location of isolated points in the point data section , so as to filter the point information of isolated area. The performance of the algorithm is verified by experiments. The results show that the filtering method can filter all the isolated data. At the same time, the class I error and class III error are less than 1%, and the filtering has little impact on the characteristics of the main point cloud.It meets the application requirements of Point Cloud Filtering in medium and large measurement fields, and has good engineering application value.