It was discussed the proper choice for processing and welding technology of large thin-wall steel caisson in Taizhou Bridge. According to the caisson's characteristics of large size and thin wall, reasonable welding and assembly methods were adopted to effectively control precision in the processes of fabricating and assembling pieces of each unit and the whole caisson, and the welding and anti-deformation precision of thin-wall steel sheet can be controlled too. Thus the processing quality was guaranteed.