Abstract: This paper takes the construction of a steel box girder in the Dianmian Avenue Expressway Construction Project (Phase I) as an example,and introduces the use of steel box girder dislocation division,longitudinal division,horizontal division,and unit pre-assembly under the conditions of a narrow urban site,the welding forming method of the steel box girder with pre-fixed joints and temporary support at the bridge position.Use MidasCivil software to establish a spatial finite element model,and perform finite element analysis on the stress and deformation of the steel box girder unit during transportation and hoisting, as well as the overall structure strength,stiffness and stability of the temporary support frame.The results show that the corresponding stress and deformation are both Meet the specification requirements.This summarizes the key construction technologies of steel box girder segmentation,linear control,temporary buttress design, installation and welding, etc,in order to provide reference for the construction of similar projects in the future.