Abstract: A new form function involving parameters β₁ is presented. On the basis of the form function, an initial form of tension structure was found by interpolating through the control points on boundary of the structure. The form function can be controlled by changing β₁ according to the pre-tension and the boundary of the structure. The final form of a tension structure should be an equilibrium system under the pre-tension. To examine the nature of the initial form, the FEM was used. Many examples show that the initial form gives a very ideal result for equal or unequal pre-tension in two directions of the structure. In general cases, there is little difference between the initial form and the final one.