Abstract: Forms of tensile membrane structures cannot be arbitrarily selected, therefore, the first step of designing these structures is to determine surfaces that satisfies static equilibrium and architecture need. Firstly, the initial equilibrium problem for tensile membrane structures is described. Then, geometrically nonlinear finite element equations for analyzing membrane structures are presented. A method for form finding of tensile membrane structure, is presented. The determination of pre-stress in membrane structures is discussed and convergence criteria for form finding are suggested. Some examples of form finding are given, indicating that the present method is effective.