A novel, cheap and high-efficiency nanocomposite Ni-Co/Mo2C/Co6Mo6C2@C has been successfully constructed through simple one-step carbonization method (N2). Due to the fact that polyethyleneimine (PEI) in the precursor can effectively anchor molybdenum-based Keggin-type polyoxometalate (PMo12) and layered double hydroxide (NiCo-LDH) through electrostatic and coordination interactions, it can avoid the aggregation of catalyst particles during the pyrolysis process. After the optimization, the obtained Ni-Co/Mo2C/Co6Mo6C2@C possesses small size (3-8 nm, concentrated at about 4.5 nm), large specific surface area and hierarchical pore structure. More important, Ni-Co/Mo2C/Co6Mo6C2@C presents remarkable hydrogen evolution reaction (HER) activity with low overpotentials in 0.5 M H2SO4 (102.3 mV) and 1 M KOH (95 mV) to afford the current density of 10 mA·cm-2, as well as small Tafel slopes of 82.49 mV dec-1 and 99.92 mV dec-1, respectively. Simultaneously, this catalyst also shows outstanding stability for 12 h without significant change in current density. Herein, such excellent catalytic performance of Ni-Co/Mo2C/Co6Mo6C2@C can put down to the synergistic effect between multiple components and the small size of the catalyst. This work provides unique insights into the preparation of efficient transition metal-based catalysts for HER.