The development of flexible manufacturing creates new problems for U-bolt tightening. A fully automatic U-bolt tightening machine was designed. Modular system architecture was adopted to design the tightening machine. A separated functional design was used to tightening shaft and the auxiliary displacement mechanism design. The machine was combined with the enterprise MES system to realize automatic U-bolt tightening. Based on analyzing the system control principles and introducing the actual working process, a Ethernet bus based bolt tightening machine control system solution was presented.