Based on the application research of 3D laser scanning technology in railway tank car, the problems of incomplete point cloud and noise which were found during the scanning process were analyzed, and a fast and effective optimized processing method of point cloud was proposed. The new method included sp-H point cloud pre-processing method and Eti-G modeling optimization key algorithm. The verification test results show that the new optimized processing method of point cloud can be used to optimize the noise and incomplete point cloud in a relatively short time and can fast and efficiently reconstruct the model, which improve the applicability of scanning the point cloud under different working conditions, and the efficiency and accuracy of scanning work are also promoted. The related expanded uncertainty of volume measurement results of railway tank car reaches 2.4×10^-3, which is the highest accuracy level of railway tank car volume scanning, and provides some references for the development of 3D laser scanning technology.