Long span structures like space-structures have instability phenomenon, jump buckling or bifurcation. And these instability phenomenon responds very sensitivity, depend on the initial condition. In this study, define the 1-degree of freedom space structure and when model has beating load, analysis critical load of model using 3D contour map for load, variable , displacement in the axial. The analysis results, when  is 1.0, is able to see the lowest critical load and the resonance phenomenon.