The absorption behaviors of CO on the (8,0) semiconducting intrinsic and gold doped (Au-doped) single-walled carbon nanotubes (SWCNTs) are investigated by the density functional theory because superior sensitivity of carbon nanotube to many toxic gases becomes a field of growing interest. It is shown that CO molecules can be absorbed to Au atoms on the wall of Au-doped SWCNT with a bingding energy as high as 2.1eV,and can attract lager charge transfer 0.23. Compared with the intrinsic SWCNT, the Au-doped SWCNT presents a high sensitivity to CO in terms of the calculated geometrical structures and electronic properties, Furthermore, the calculated electron densities of two representative adsorption positions show that Au-doped SWCNT electron clouds overlap more on the top of carbon adsorbed CO. By comparison with the oxygen absorption on SWCNT, we infer that the molecular CO absorbed on Au-doped SWCNT can induce significant change in the conductivity of SWCNT. So Au-doped SWCNT is expected to be a potential candidate for detecting the presence of CO.