This paper developed finite volume method program with Smagorinsky sub-grid scale model using 3-dimensional unstructured mesh to accurately determine the flow field characteristics behind a cylinder in sub critical region and the applicability of 3-dimensional large eddy simulation method of this kind of calculation based on C++ programming language. Numerical simulation was performed for the flow over a circular cylinder at a classical sub-critical Reynolds number (Re=3 900) using a new second order defer correction scheme for unstructured mesh. The results show that mean and fluctuating flow characteristics were compared well with the existing experimental results, 2-order discretization scheme large eddy method can be used in the simulation of sub-region Reynolds number outer flow simulation. The results also proved the reliability of high accuracy and stability discretization scheme.