[en] KOPEC has been developing a two-phase thermal hydraulic solver for the safety analysis of nuclear power plants. The pilot code adopts the multi-dimensional, three field governing equations. Several numerical schemes, such as collocated, staggered, semi-implicit, and implicit schemes, have been tried so far. Among the various numerical solution schemes implemented in the pilot code, the staggered mesh semiimplicit and implicit schemes are formulated using the orthogonal hexahedral mesh. This mesh system is a little inconvenient to represent complex geometry, compared to the general polyhedral mesh. However, the hexahedral mesh is useful to generate 1-D, 3-D Cartesian, cylindrical, spherical meshes, which can cover most of the geometry encountered in nuclear power plants systems. It is also noticeable that this type of mesh can be easily generated on an algebraic basis, on the contrary to the general polyhedral meshes which generally need mesh generator like GAMBIT. In this paper, a simple algebraic way to generate the 1- D, 3-D Cartesian, and cylindrical block meshes will be described. In addition, a methodology to construct complex system will be demonstrated by connecting the already generated block meshes with the block linkage data provided by users