For the first time, a porous CoSe2/C microsphere interwoven by ultrathin CoSe2 and carbon nanosheets is synthesized by a simple solvothermal method. Compared with bare CoSe2, the CoSe2/C hybrid exhibits much better performance for hydrogen evolution reaction (HER): The hybrid demonstrates a Tafel mechanism rather than the Heyrovsky mechanism of CoSe2; it has a low onset potential (- 189 mV vs RHE) and an ultra-low Tafel slope (34 mV dec(-1)); current density increases by more than 2.5 times at equipotential; the hybrid also exhibits remarkable long-term stability even after 1000 cycles. At root, the superior HER performance of CoSe2/C stems from its unique porous microsphere intertwined by ultrathin CoSe2 nanosheets and conductive carbon nanosheets, which not only facilitate the electron transfer and ion diffusion, but also produce abundant electrocatalytic active sites for HER. This facile and scalable synthetic method can be extended to synthesize nonprecious transition-metal-based catalysts with unique nanoarchitecture and outstanding HER performance.