In order to meet the requirement of micron scale measurement for many small industrial parts, a measuring method combining point cloud multiple filtering and plane fitting was proposed.A 3D line laser sensor was used to obtain the point cloud model of the regular triangular prism, which was parallel to the upper and lower planes, and the point cloud model was transferred to the computer for processing. Firstly, the noise and outliers were removed by statistical filtering.Secondly, the number of point clouds is reduced by voxel filtering and down-sampling.Then the upper and lower surfaces of the workpiece point cloud are separated by straight-through filtering.Then, the point clouds on the upper and lower surfaces are fitted with the plane equation by RANSAC algorithm.Finally, the distance between the upper and lower planes is calculated as the height information of the measured workpiece.The height measured by this method is compared with that measured by laser triangulation. The results show that the accuracy of this method is improved by 72.33%.At the same time, for different point cloud densities, the proposed method is used to measure, and the measurement error is minimum when the side length of the voxel cube in the sample is 15cm (when the number of point clouds is reduced by 98.3%), and the minimum can reach 5.1𝜇m.This method greatly improves the measuring accuracy of workpiece and can be widely used in industrial measurement.