Abstract: Taking the mechanical seals with complicated structures as the study object, the dimensionless mathematical model for the torsion deformation of the dry gas seals (DGS) at high pressure was presented based on circle theory and gas lubrication theory. The calculating method for the torsion deformation caused by the film pressure was present. The influence rules of the construction and position of secondary seals ring on the torsion deformation based on optimum method of multi-factor was studied. The results show that the analytic method and concentration method were feasible. The influence rules and degrees of various structure parameters on the torsion deformation of seal were different. The torsion angle increased with the increasing step to outer radius ratio π₂、step length ratio π₃、length ratio of the position of secondary seal ring π₅. The torsion angle decreased with the strengthen of width ratio of step π₄ and inside radius r_i. When π₄≤3.5, the torsion angle decreased with the increase of length-width ratio of step π₁. When π₄>3.5, the torsion angle increased first and then decreased, and the torsion angle was in the maximum when π₁=2~3. Compared with the influence of π₂, the torsion deformation was less affected by the influence of π₁. Compared with the influence of π₁, π₂, π₃, π₄, r_i and π₅ had little influence. The influence of position of secondary sealing ring on torsion deformation had little influence compared with the influence of structure parameters.