A novel and highly active vanadium self-intercalated C/V_1.11S₂ nanosheets with abundant active sites are fabricated by a simple hydrothermal-calcinations method. The structures and morphology of C/V_1.11S₂ nanosheets were characterized by XRD, SEM, XPS and TEM. Particularly, PVP (polyvinylpyrrolidone) was used as surfactant to control the morphology of vanadium sulfide and carbon source to reduce the vanadium sulfide into vanadium self-intercalated V_1.11S₂ phase with rich active sites. The C/V_1.11S₂ nanosheets showed an excellent electrocatalytic activity for hydrogen evolution reaction, including a low onset potential of 15 mV vs. RHE (reversible hydrogen electrode), small Tafel slope of 51 mV dec⁻¹, as well as extraordinary catalytic stability. The first-principle calculations further confirmed that the V_1.11S₂ has a much lower Gibbs free energy for hydrogen adsorption (ΔG_H) than that of VS₂. The enhanced HER performance can be contributed to the unique vanadium self-intercalated structures, nanostructured morphology and rich sulfur defects of the obtained C/V_1.11S₂ nanosheets. We believe that the C/V_1.11S₂ can be used as electrocatalyst in chemical engineering industry and our method provides guidance on the fabrication of other defective transition-metal dichalcogenides to improve their catalytic performances.