It is of significant academic value to find a new type of eco-friendly photocatalyst with high-efficiency, low-cost, which can be applied to the photocatalytic synthesis of N-2/H2O to ammonia. In this paper, pitch-based graphene oxide (GO) is obtained by using petroleum pitch as a carbon source (Hummers Method). Then, the ZnS nanoparticles were loaded onto the pitch-based GO sheet to get the composite photocatalyst ZnS/GO of different GO contents (Hydrothermal Method). The performance of ZnS/GO photocatalytic synthesis of N-2/H2O to ammonia was studied while characterizing the material structure and photoelectric properties. The results showed a similar structure and performance with general graphite-based GO. The presence of GO structure not only enables the composite catalyst to enhance electron transfer by inhibiting the recombination of the photogenerated electrons and holes pairs, but also improves activation and adsorption N-2 properties and photocatalytic ammonia synthesis with N-2/H2O performance. The NH4+ yield was 910.6 mu mol/L.g cat after 6h photocatalytic reaction, which was about five times of NH4+ yields on pure ZnS as a photocatalyst under the same conditions.