The interaction between electrocatalytic active centers and their support is essential to the electrocatalytic performance, which could regulate the electronic structure of the metal centers but requires precise design. Herein, we report on covalent grafting of graphene quantum dots (GQDs) on stepped TiO2 as a support to anchoring cobalt phosphide nanoparticles (CoP/GQD/S-TiO2) for electrocatalytic hydrogen evolution reaction (HER). The covalent ester bonds between GQDs and TiO2 endow enlarged anchoring sites to achieve highly dispersed electroactive CoP nanoparticles but, more importantly, provide an efficient electron-transfer pathway from TiO2 to GQDs which could regulate the electronic structure of CoP. Therefore, such CoP/GQD/S-TiO2 exhibits a superior electrocatalytic HER performance compared with CoP/S-TiO2, exhibiting a mass activity which is 6.3 times that of the CoP/S-TiO2 counterpart and long-term stability over 100 h electrolysis. Mechanistic studies reveal that sufficient electron transfer occurs from TiO2 to the π-conjunction in GQDs via the Ti-C-P pathway and further injects into grafted Co centers, inducing the formation of electron-rich Co centers to enrich and stabilize the hydrated alkaline cations (AC+) for facilitated alkaline HER kinetics. Our study provides a new idea for electronic structure engineering of catalysts via covalent bonding toward boosted electrocatalysis.