In order to study the influence of various factors on the nonlinear stiffness of bolted flange connection structure，a fine finite element model of screw connection structure with rising angle was established，the full hexahedron mesh generation was carried out，and the validity of the model was verified.The simulation analysis under tension，bending and torsion load was carried out respectively.The results showed that the larger initial pre-tightening force indicated the greater bending and torsional stiffness of the connection structure，and the initial pre-tightening force had no influence on the tensile stiffness.Under the tensile load，the initial preload increased the critical resistance of the separation of the two flanges.Under the bending load，the greater initial preload indicated the greater external bending moment triggering the opening of the two flanges，and it was more difficult for each bolt to bear the external force.Before the opening of two flanges，the initial pre-tightening force had little influence on the bending stiffness of the connection structure，but the influence was greater after the opening；the larger diameter and more number of bolts indicated the greater tensile，bending and torsional stiffness of the connection structure；the closer bolt position to the flange tube indicated the greater tensile stiffness of the connection structure.The friction coefficient between the joint surfaces had no influence on the tensile and bending stiffness of the connection structure.The greater friction coefficient between the joint surfaces indicated the greater torsional stiffness of the connection structure.The friction coefficient between the flange and flange joint surface had a greater influence on the torsional stiffness in the first section of the stiffness curve，while the friction coefficient between the bolt flange joint surface had a greater influence on the second section.