In order to obtain the theoretical simplified and calculation method of bolted joints under eccentric load, the static load test, theoretical calculation and finite element analysis of bolted beam reaction system are carried out. Through theoretical calculation and finite element analysis, the irregular variable section of reaction beam is equivalent simplified, and the structural combination coefficient k of steel structure reaction beam is proposed, which can quickly and accurately calculate the moment of inertia of irregular variable section beam. Based on this, the theoretical simplification and calculation method of bolted joints are solved by test and theoretical calculation. The results show that in the theoretical calculation, the bolt joint is simplified to a fixed support, and the correction coefficient ki is introduced to correct the theoretical results, which can well reflect the actual deflection deformation of the reaction beam, and its correction coefficient can provide a reference for the designers of subsequent bolt connection.