Although Mo-dependent nitrogenase and synthetic molecular complexes have attracted widespread attention in electrochemical nitrogen reduction, the activity of Mo-based catalysts for nitrogen reduction is low. Herein, molybdenum oxide nanoparticles were supported on charge-modulated conjugated triazine frameworks (Mo/CTF-I) via ion exchange reaction. Compared with Mo/CTF, the modified Mo/CTF-I maintains high specific surface area and microporous structure after metal loading and thermal treatment, and exposes high density MoOx as active sites. This strong interaction between MoOx and CTF-I induces the electron transfer from Mo to support to form MoOx with a valence state of 5+ and lowers the energy barrier to transfer the donated electrons to the empty anti-bonding π orbitals of N≡N. Electrochemical measurements proved that 5% Mo/CTF-I exhibited the highest NRR activity with a faradaic efficiency of 27.3% and an NH3 yield rate of 7.23 mg h-1 gcat.-1 at -0.405 V vs. RHE.