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The embedded atom method was used to theoretically analyze the effect of the lattice parameter variation on the order-disorder transformation in binary alloys. The simple model was considered in which the configuration energy E as function of the lattice parameter a and the long-range order parameter sigma was given by Taylor expansion at sigma =0. The following results were found for AB alloy, at T=0 K, the stable state exists in the completely ordered phase which was also found in the case of A(3)B or AB(3) compounds The order-disorder was found to be a second-order transition. Only one kind of order-disorder was found for AB alloy. Three groups of order-disorder transformation can be observed for the A(3)B or AB(3) compound. For the group I when the temperature is below the critical temperature, the order-disorder is a first order transformation. For the group II, the order-disorder transformation is a first order transition. For the group III, the order-disorder transformation is found to be a second order transition. The lattice parameter variations have a significant effect on E-2 coefficient, which is related to the ordering energy. These results are, in a good agreement with those obtained by using EAM (embedded atom method) and CVM (cluster variation method), calculations.