To solve the problems of site occupation and long construction cycles of physical trial assembly（PTA）during bridge construction，the intelligent virtual trial assembly（VTA）method for large and complex box girders was proposed based on point cloud data（PCD）. The connection pattern of the box girder was analyzed to establish the technical framework and the flow of methods for the VTA. Considering the quality control accuracy of box girder segment machining，the algorithm for beam axis direction vector extraction was developed based on the characteristic plane. The PCD matching methods was also analyzed, and the computational complexity was reduced based on prior knowledg. Taking the Ziyun Bridge in Fengcheng City, Jiangxi Province as the engineering background, the virtual pre assembly technology was verified.the research results show that the intelligent VTA method proposed in this paper is charactered as high degree of automation. That does not depend on the 3D model. The proposed method can effectively guide the correction of dislocation in the butt joint section of adjacent steel box girders，improving the construction efficiency. This study can provide theoretical support and technical reference for the digital construction of similar structures.