In this paper molecular dynamics (MD) method and the modified analytical embedded atom model (MAEAM) are used to investigate the size effect on the elastic properties of Ni, Al and V nanowires and the role the free surface plays. For convenience of comparison, the elastic properties of these corresponding perfect bulk materials are also studied. Results obtained indicate that the calculated values of the elastic properties of these perfect materials are in good agreement with those previously given theoretical and experimental ones. But the calculated bulk moduli of the nanowires, which are lower than those of the prefect materials, increase exponentially with increasing size of the nanowire and are nearly close to a constant (180.20 GPa for the Ni nanowire, 83.98 GPa for the Al nanowire and 162.48 GPa for the V nanowire). Meanwhile, the surface energy of the nanowire decreases exponentially with the increase of its size and reaches a minimal value (1.84 J·m-2 for the Ni nanowire, 0.77 J·m-2 for the Al nanowire, and 1.71 J·m-2 for the V nanowire), which is consistent with the corresponding bulk material. And the critical value of the size, which has a distinct effect on the elastic properties and the surface energy, is about 5.0 nm for all nanowires. On this basis, the free surface dependence of the elastic properties of these metallic nanowires and the inherent mechanisms are further discussed by exploring the size effect on the surface energies of Ni, Al and V nanowires and their distribution characteristics, showing that the free surface plays a more and more important role in the diminution of the elastic properties of nanowires as the size decreases. The mode of the surface impacting on the elastic properties of nanowire is described as follows:The surface first reduces the compressional stress of the internal core region of nanowires and then the reduced compressional stress results further in the decrease in the elastic properties of nanowires.