Using density functional theory and nonequilibrium Greens function, the electronic structure and transport properties of chiral (6, 3) single-walled carbon nanotubes substituted by nitrogen atoms were investigated. The results show that the configurations and the concentration of the doped atoms have complicated effects on the transport properties of the chiral single-walled carbon nanotubes. The electronic structures of the carbon nanotubes are changed obviously. The transportation properties are degraded by the doping of nitrogen atoms and change significantly with the positions of impurity atoms in the structure. The currents-voltage curve shows nonlinear variation. Under certain conditions the metallic single-walled carbon nanotubes may be converted into semiconductors.