Steel Bridges are temporarily assembled in shop yard at the final stage of member fabrication, so as to ensure the accuracy and connectivity of members. This process, shop assembly, demands huge shop yard and tremendous labor. In order to settle this problem, the authors have developed a system that performs the simulation of shop assembly, instead of assembling members in shop yard. This system consists of two subsystems which are measuring system and simulation one. The authors performed an experiment on the composit girder to demonstrate the validity and applicability of the system. The reliability of this system is verified through the experiment.