The wide use of air laser scanning for the building of digital terrain models in Russia has been used for more than 20 years. To process the results of air laser scanning, it is necessary to classify the points of laser reflections. Classification of laser reflection points is carried out by international commercial software products, often using algorithms of rarefaction of the “Earth” class data, which does not consider the features of the relief shape. In the paper, it has been proposed a proprietary algorithm for interpolating laser scanning data, which allows the removal of redundant points of “Earth” class laser reflections with a primarily reduction in the detail of the flat terrain data. A distinctive feature of the proposed solution is its low computational complexity. This allows the algorithm to work effectively with large arrays of data, obtained during air laser scanning. The paper presents a detailed step-by-step description of the algorithm operation, as well as the results of the digital relief model building based on a cloud of laser reflection points of the Earth class, processed using the proposed algorithm.