Abstract: According to the thermodynamic and mathematical properties that the stable area of the substance in the phase diagram of the area of predominance is defined by the solution of linear inequalities and it's geometrical shape is convex polygen, the new computer algorithm of the calculation for the phase diagram of the area of predominance is developed in this paper by the solutions of the problems of linear programming that is made by introducing a series of optimum functions to the linear inequalities. The FORTRAN program has been made by the use of the Revised Simplex Method that is used for computer to solve the problems of linear programming. The results cal- Ciliated by this method is correspond to the papers published. The method has the following advantages, such as has definit, clear and reliabl e mathematical model; clear physical concept; appropriate for common use; high accurate in results and more convienent to the very complex systems.