In the present paper, superlattice phase transition and toughening of intermetallic compo-unds are studied. By writting the Hamiltonian of superlattice phase transition as the Ising's one, the expression of short-range-order parameter in superlattice phase transition P′ =1-exp (-2J/kT) is derived based on the correspondence of Ising model and bond percolation. The phase transition points of superlattice phase transition for systems with L10 and L12 structures are ther obtained by Monte-Carlo simulation, which is P′bc = 0.3436 (for Llo structure), P′bc= 0.4924 (for L12 structure). Furthermore, the relationship between P′bc and the corresponding values Pbc of general percolation process with the same nominal structure P′bc x=Pbc is for-mulated. Finally, the influence of composition variable x to the phase transition point, the or-dering and the brittleness of intermetallic compounds is expounded theoretically. It provides the theoretical basis for the toughening of intermetallic alloys, and also enriches percolation theory.