This paper mainly discusses the application of three-dimensional laser tracking technology in the installation of pressure vessels in nuclear power plants. In order to meet the high-precision requirements of the installation of the main system equipment in nuclear power plants, control the manufacturing error of the equipment body, reduce the impact of the equipment body deviation on the later installation, obtain the measurement data required for processing in advance, and shorten the on-site construction time, it is necessary to measure the body size of the pressure vessels before leaving the factory. This method is mainly based on the advantages of high accuracy and efficiency of 3D laser tracking technology in the measurement of large size workpieces. Through the analysis and research of key construction technologies such as instrument station, common point layout of transfer station, measurement feature point selection, data acquisition method, data processing method, etc., the size data of pressure vessel body is finally obtained. Comparing it with the relevant design data, the size data required for on-site installation is calculated, so as to achieve accurate measurement and efficient processing of the size data of the pressure vessel body, providing reliable technical support for subsequent on-site construction.