The evaluation of the reliability of structural systems is of extreme importance in structural design, mainly when the variables are random. A method is presented to efficiently assess the random response of stochastic structures. The article uses two-level sampling method to partial fiber element. First, the homogeneous random field of concrete and rebar can be created by modified Latin-hypercube sampling. Then section discretization method is adopted to assign fiber random variables of concrete section fiber. The algorithm is then used to analyze the random response of a concrete beam, and the result proves that the method is efficient.