We investigate the scanning tunneling microscopy (STM) tip-modulated atomic motion on the top of Co island and interlayer mass transport on the island edge based on the molecular static (MS) method. Our results show that STM manipulation has an important effect on Co atomic diffusion on the top of Co island and on the island edge. The interaction of the STM tip with the adatom and the strong shape transitions in Co island and in the Cu(001) substrate result in the change of the jump diffusion barrier on the top of the island, the Ehrlich-Schwoebel(E-S) and exchange barrier on the island edge. It is found that by adjusting the distance between the tip and the substrate one can reduce the diffusion barrier of the above three diffusion processes and transform the growth mode of the Co films from 3D to 2D.