In this paper the molecular dynamics (MD) technique and the modified analytic embedded atom method (MAEAM) are applied to study the influence of size and surface condition of the nanofilm on the elastic properties of B2-NiAl, The elastic properties of the bulk NiAl alloy and the size dependence of the surface energy of nanofilms are first calculated. It is found that the calculated results of the elastic properties are consistent with those from experiments and theories; and the surface energy, which is barely influenced by the thickness, is controlled by the surface atomic composition. On this basis, our investigations are mainly focused on the relationship between the elastic properties of nanofilms and their thickness. The obtained results indicate that the elastic properties of the nanofilm may change exponentially with the increasing thickness, which can also be regulated by the surface atomic composition. Furthermore, the inherent mechanism of the thicknes and surface that affects this relationship is analyzed in detail, showing that the surface atomic composition and the deviation of interplanar spacing in nanofims are two major factors for determining the thickness dependence of the elastic properties. These are in good agreement with the previous theoretical and experimental studies.