A detailed knowledge of the structure and composition of NiAl compound is essential for understanding its oxidation resistance and the fracture process. The atomic distribution, concentration and long range order parameters in interior and (110) surface layer of NiAl compound at 1273 K are calculated by the grand canonical Monte Carlo simulation method. We find a quasi-exponentid relationship between the component deviations from the stoichiometry in surface layer and interior of NiAl in Al-rich region. It is observed that the deviation of component from stoichiometry in surface layer is over 30 times greater than that in interior.