Based on the conditional expectation variance reduction, antithetic variable sampling and Neumann expansion technique,and in order to solve the problem of uncertainty of strength model partly,considering the different characteristics of uniaxial compressive strength σc and bidirectional isobaric strength σcc of concrete and rock materials, this paper applies 3 parameter unified strength theory to FEM program，and Monte Carlo 3 D nonlinear stochastic FEM model for structure reliability analysis is constructed. The result shows that this model has nice convergence, high efficiency, low cost and enough precision of index β for practice. The model is valuable for large-scale complex structure design and reliability analysis.
