In alkaline media, slow water dissociation leads to poor overall hydrogen evolution performance. However, Ru catalysts have a certain water dissociation performance, thus regulating the Ru-H bond through vacancy engineering and accelerating water dissociation. Herein, an excellent Ru-based electrocatalyst for the alkaline HER has been developed by incorporating Ru into Se vacancy-containing CoSe (Ru-V-CoSe). The results from X-ray photoelectron spectroscopy, kinetic isotope effect, and cyanide poisoning experiments for four catalysts (namely Ru-V-CoSe, Ru-CoSe, V-CoSe, and CoSe) reveal that Ru is the main active site in Ru-V-CoSe and the presence of Se vacancies greatly facilitates electron transfer from Co to Ru a bridging Se atom. Thus, electron-rich Ru is formed to optimize the adsorption strength between the active site and H*, and ultimately facilitates the whole alkaline HER process. Consequently, Ru-V-CoSe exhibits an excellent HER activity with an ultrahigh mass activity of 44.2 A mg (20% PtC exhibits only 3 A mg) and a much lower overpotential (29 mV at 10 mA cm) compared to Ru-CoSe (75 mV), V-CoSe (167 mV), CoSe (190 mV), and commercial Pt/C (41 mV). In addition, the practical application of Ru-V-CoSe is illustrated by designing a Zn-HO alkaline battery with Ru-V-CoSe as the cathode catalyst, and this battery shows its potential application with a maximum power density of 4.9 mW cm and can work continuously for over 10 h at 10 mA cm without an obvious decay in voltage.