Abstract: The effective atom model based on EAM potential was applied to study the relationship between the structural stability and the long range order parameter of non-stoichiometrical Ni₃Al based alloys. The calculated results indicate that the order-disorder transition temperature (T_t) increases with Al composition increasing. The order-disorder transition process is a nucleation-propagation process. The microstructure of partially order state is a mixed microstructure with full disorder and full order domains. The calculated results are consistent with the experimental results.