- An effective potential approach to the description of the ordering in alloys is suggested. It allows to describe the changes in phase relations when the temperature is growth on the basis of the calculations of the ground state energies of ordered phases. The static concentration waves theory of Khachaturyan is used for the evaluation of the internal mixing energy of alloy. The suggested model outlines the technique to calculate the values of the energy parameters of ordering process from the first principles. For the analysis of this parameters as well as for the estimation of the temperature dependences of the long-range order parameter in NiTi the total energy Full Potential LMTO calculations were used.