Based on the bolt preload equation,the relationship between tightening moment and preload of the pipeline connection structure was deduced,the finite element model of the pipeline connection structure was established,and the relationship between torque and preload of composite pipeline connection structure was simulated and calculated theoretically.The relative error of the calculation results between the established finite element model and the theoretical formula is small,which verifies the validity of the finite element model.Based on the tightening model of the pipeline joint structure,the influence of the angle error on the tightening process and sealing performance was studied.The results show that the tightening process with angle error is divided into nonlinear fitting period and linear tightening period.With the increase of the angle error,the width of the sealing ring decreases,and the width of the sealing ring of the large ball decreases faster than that of the small ball.As the angle error increases,the preload of the composite pipeline joint structure decreases,and its assembly cannot achieve the expected effect.