To search for efficient electrocatalyst towards ORR and OER for sustainable energy conversion, storage, and utilization, a family of single transition-metal atom (Mn, Fe, Co, Ni, Cu and Zn) doped two-dimensional tungsten disulfide monolayers have been systematically investigated by using first-principle computations to uncover the impact of transition-metal dopants on ORR and OER electrocatalytic activities. It is demonstrated that single-metal-atom sites can bind to the surface of 2D WS2, enhancing the adsorption of intermediates involved in the OER/ORR and decreasing overpotentials effectively. Compared to the pristine 2D WS2, most of transition-metal doped catalysts can decrease overpotentials and promote OER and ORR activities effectively. Particularly, Ni@WS2 and Zn@WS2 are screened out to exhibit the best electrocatalytic activity among all systems with an overpotential of 0.33 and 0.47 V for OER process, respectively, showing that Ni@WS2 and Zn@WS2 are potential candidates for OER electrocatalysts. Furthermore, their electrocatalytic performance are explained in terms of volcano plot, scaling diagram, d-band center model, and charge analysis.