Multiscale simulations using the quasicontinuum (QC) method with the embedded-atom method (EAM) potential are performed to investigate the process of nanocontact including sliding and subsequent withdrawal between Ni tip and Au substrate. The multiscale model reveals that deformation twinning in Au substrate is induced not only by the sheer stress but also by the adhesive stress. Combining with the generalized planar fault energy (GPF) curve of Au, the underlying formation mechanism of deformation twinning is studied in detail. During the withdrawal process, the dislocation degeneration and the vacancy evolution are observed.