Abstract: A method of constructing and computing the Voronoi polyhedron of every ion in the simulation unit cell extended with periodic boundary condition directly by definition without resorting to any similarity, so called successive cutting method is described. According to the phase orbit t by the simulation of LiCl system with molecular dynamics method and considering the periodic boundary condition, more than 20,000 Voronoi polyhedrons have been constucted and computed, At each of the following temperatures, 900 K, 698 K, 498 K and 298 K, we have calculated about 5,000 Voronoi polyhedrons. The results of statistical analysis of all information about these Voronoi polyhedrons including the number of side faces, volume, vertex, edge, and poly n of side face are reported. The statistical analysis shows clearly that different phase of the LiCl system possesses different character of the local structure. It merits our attention that at 298 K the distribution of the numbers of side faces of Voronoi polyhedrons is very concentrative. Therefore we define the coordinaton number of Li~+ ion and Cl~- ion by the volume and its component of the Voronoi polyhedron. The coordination number and its composition had baen evalua ted too.