Abstract: As a key bearing member of stretch forming lattice structure(SFL),the upper chord ring beam is a cross center of all radiating upper chord beams.In order to deeply understand the displacement character of SFL affected by upper chord ring beam, six mechanic models about SFL,whose rigidity are monotone increasing,are established on the basis of ANSYS finite element program,which selects two tensioning method-tensioning simultaneously step by step and tensioning group by group and step by step.So the displacement rule affected by upper chord ring beam is concluded.When the construction method-tensioning group by group and step by step is chosen,the overstepping or lagging displacement on structural nodes belonging to different group inevitably comes into being,which is different from the method of tensioning simultaneously.The study shows that properly reinforced upper chord ring beam will weakens the displacement difference in a great extent,and it is favorable to SFL forming.