Because of its advantages such as abundant resources, low cost, simple synthesis, and high electrochemical stability, cobalt phosphide (CoP) is considered as a promising candidate for electrocatalytic hydrogen evolution reaction. Through element doping, the morphology and electronic structure of the catalyst can be tuned, resulting in both the increase of the active site number and the improvement of the intrinsic activity of each site. Herein, we designed and fabricated Mn-doped CoP nanowires with a length of 3 μm, a diameter of 50 nm, and the pores between the grains of 10 nm. As a highly efficient electrocatalyst for alkaline hydrogen evolution, the Mn10-doped CoP/NF (doping amount is about 10 atom %) electrode presented overpotentials of 60 mV @ 10 mA cm-2 and 112 mV @ 100 mA cm-2, improved by 35 and 23%, respectively, compared with CoP/NF. Characterizations indicate that Mn doping increases the electrochemical active area, reduces the impedance, and tunes the electronic structure of the material. Density functional theory calculations also revealed that an appropriate amount of Mn dopant at a suitable location can both react as an active site itself and boost the activity of the surrounding Co sites, delivering favorable H* adsorption and rapid reaction kinetics. This result may not only promote the development of hydrogen evolution reaction catalysts but also encourage explorations of the relationship between the property and fine doping structure.