Structural stability,electronic and optical properties of Ni-doped silicon nanowires are investigated by first-principles calculations based on the density functional theory. The results show that Ni can preferentially occupy substitutional sites near the surface of silicon nanowire. The doping of Ni atom in silicon nanowire introduces the impurity levels. The impurity level is mainly contributed by Ni 3d orbital. The decrease of the band gap results from the coupling of Ni 3d and Si 3p states. A strong absorption peak occurs in the low energy region of Ni-doped silicon nanowire,accompanied by the widening of the absorption band.