The invention provides a nitrogen-doped graphene coated nano sulfur positive electrode composite material, a preparation method, and an application thereof. The composite material includes: an effective three-dimensional conductive network formed by overlapping of nitrogen-doped graphenes, and nano sulfur particles coated by nitrogen doped graphene layers evenly. The preparation method includes: dispersing nitrogen-doped graphenes in a liquid-phase reaction system including at least sulfur source and acid,and depositing nano sulfur particles by an in-situ chemical reaction of the sulfur source and the acid, thereby preparing the positive electrode composite material. The positive electrode composite material of the invention has a high conductivity, a high sulfur utilization rate, and a high rate, thereby restraining the dissolution and shuttle effect in the lithium sulfur batteries, and enhancing the cyclic performance of the batteries.