Membrane structures make wrinkling by lots of various factors as eccentric force, construction errors, and fabrication errors. In this paper, we are dealing with a method to avoid numerical unstability when wrinkling analysis of membrane structure considering geometrical nonlinearity is carried out. The methods to check wrinkling by using principal stress that is proposed from this paper analyzes wrinkled element by transforming it into uniaxial element. At this point, a determination method for the range of random coefficient that is multiplied into constitutive matrix to keep the uniaxial stress in iterative analysis that counted geometrical nonlinearity. To investigate the range of random coefficient, various models are analyzed. We can figure out that 0< ${alpha}$ <0.001 is possible to carry out the wrinkling analysis without numerical unstability.