Abstract: The wrinkling analysis is critical for correctly loading analysis of membrane structures. The Principal Stress-Principal Strain Criterion which is the appropriate one for predicting the states of structural membrane: taut, wrinkled or slack, and the Modified Constitutive Relationship Method for the wrinkling analysis of membrane structures are presented. The finite element formulas are given, and the finite element program is developed on the basis of the Cable-Membrane Structure Analysis Program CAFA. The program is validated by the comparison between the numerical result and analytical solution of a stretched rectangular membrane subjected to planar bending. Results of other three example are also shown.