Abstract: In the present paper the non-linear static and dynamic post-buckling analysis of spatial frames is conducted. Based on continuum mechanics principles, the updated Lagrangian formulation is employed to develop a three-dimensional beam element which includes joint large displacements and large rotations. In material nonlinear analysis, the Mises yield criterion and Prandtl-Reuss flow rule are adopted to describe the elastic-plastic constitutive relation of the material. The Newmark integration combined with Newton-Raphon equilibrium iteration is used to solve the structural nonlinear vibration equation. The pre-buckling analysis employs the constant arc length method. The new method does not need to reduce the load in order to trace the complete load displacement curve. The applied load is increased slowly after the static critical point and the snap through process is simulated by the step by step integration method.