In the present paper, MgxZn1-xO nanofibers with different doping concentration were prepared by atom layer deposition (ALD) using polyvinyl pyrrolidone (PVP) nanofibers as template, which were synthesized by electrospinning. The influence of different Mg doping concentration on the structure and optical properties of composite nanofibers was investigated. The samples were characterized by field emission scanning electron microscopy (FESEM), ultraviolet visible (UV-Vis) absorption spectroscopy and photoluminescence (PL) spectra. The doping of Mg did not change the morphologies of ZnO nanofibers, the morphologies of all the samples were very similar while the diameter of MgxZn1-xO-PVP composite nanofibers became larger after doping. With the increase in the Mg doping concentration, the absorption edge shifted to larger energy side, revealing the band gap tenability of MgxZn1-xO nanofibers. Meanwhile, a significant blue shift of the UV emission peak from 377 to 362 nm was observed in PL spectra. Compared with ZnO-PVP composite nanofibers, the UV emission intensity of MgxZn1-xO-PVP composite nanofibers was much stronger. Component control MgxZn1-xO nanofibers can be synthesized by this method. The doping of Mg elements in ZnO can effectively improve the band gap of ZnO-PVP nanofibers and the intensity of UV emission.