Electrocatalysts for high current density hydrogen evolution reaction (HER) under alkaline conditions is critical for the widespread application of water electrolysis. Carbon-supported single-atom catalysts (SACs) stabilized by N atoms have been demonstrated as efficient electrocatalysts, but mostly for acidic HER. For alkaline HER, although defective-, edge-, and dual-sites have been found to improve the adsorption pathways of the intermediates, there is still a great challenge to precisely synthesize those complex configurations in experiments to maximize the synergistic effects. Since C atom has relatively weak electronegativity than N atom, it can induce different charge redistribution of the metal atom center. However, the reported C-coordinated SACs were derived from the N-containing precursors, which could not exclude the influence of heteroatoms on the activity completely. Herein, we reported the synthesis of carbon-coordinated CoC4 sites and ultra-small Co cluster directly embedded on pure carbon cloth (Co-SA/CC) via the high temperature shockwave (HTS) method. The C atoms on the first coordination shell can tune the local electronic structure and up-shift the d-band center of the Co atom, thus strengthening H2O molecule adsorption and promoting water dissociation. The self-supporting electrode with CoC4 can lower the interfacial contact resistance, leading to higher HER performance compared with that of Pt/C at high current density (e.g. 1000 mA/cm2). These results provide a new insight into the fundamental understanding of design and synthesis of C-coordinated atomically dispersed catalytic sites.