Abstract: The force-density method can simplify the form finding process of membrane structures via the concept of force density. However, the value of force density has to be determined through several trial calculations, which greatly depends on personal experience and may result in the process of form finding being inefficient and even invalid. The modified force-density method is proposed in order to overcome the disadvantages of the force-density method. A form-finding experiment of the membrane structure using Fluotop T2 is conducted to verify the modified force-density method. The tensioning process in the experiment followed the tensioning technology of the actual project. It is a saddle-shaped tensile membrane with plane size of 4m×4m, 4 cable boundaries and 4 supports. The tension process is controlled by both strains of the cable and displacements of the membrane. The cable strains, the membrane strains and the coordinates of several points on the membrane surface in three states, named zero-state, intermediate-state and final-state, are selected to be measured. By comparing the membrane surface strains, cable strains and the coordinates of testing points in the experiment results, calculation results, ANSYS results and analytical results, the modified force-density method is verified and can be used in form-finding analysis of practical membrane structures. Moreover, some experiences and lessons in measuring the strains of membrane surface are summarized.