The storage capacity of underground liquefied petroleum gas (LPG) watersealed cavern has to be measured after acceptance. In this paper, the measuring model of Huangdao underground LPG watersealed cavern is decided； and then the factors effecting the storage capacity of cavern during crosssection measurement are analyzed; the combination application of Grade I highprecision automatic total station, tunnel crosssection measuring system and 3D entitative modeling software is discussed; the artificially calculated results and the modelling automatic calculation results based on data collected are compared with results from the third party. Finally, a 3D model of the cavern is established； and a series of achievement is obtained. The results show that the crosssectional measuring method is feasible and convenient, and it can meet the precision requirements of storage capacity measurement.