Abstract: A new form function involving parameters B i 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 Biaccording to the pretension and the boundary of the structure.The final form of a tension structure should be an equilibrium system under the pretension.To axamine 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 pretension in two directions of the structure.In general cases,there is little difference between the initial form and the final one.