Electrocatalytic　reduction　of　nitrate　to　ammonia　is　an　effective　method　for　the　recycling　of　NO3--N　in　the　field　of　nitrate　polluted　water　treatment.　In　this　work,　Co-N-C　was　prepared　in　this　work　by　pyrolysis　of　Co-based　metal　organic　framework　at　700　degrees　C　and　it　can　achieve　100　%　selectivity　to　ammonia　under　the　optimum　experiment　conditions.　Impressively,　no　harmful　nitrite　generated　in　the　reduction　process　because　the　reduction　rate　constant　of　Co-N-C　for　NO2-　-N　is　higher　than　that　of　NO3-　-N.　Experiment　results　show　that　the　chemical　adsorption　rather　than　electrostatic　adsorption　dominated　among　Co-N-C　and　free　NO3-　,　which　is　significant　for　the　subsequent　electronic　reduction　process.　Mechanism　analysis　indicated　the　active　hydrogen　(H*)　reduction　mechanism　is　predominate　for　Co-N-C　but　the　direct　electron　mechanism　is　predominate　for　Co-C　during　the　reduction　from　NO3-　to　NO2-　.　While　for　Co-N-C　and　Co-C,　the　subsequent　reduction　of　NO3　to　NH4+　was　conducted　by　the　direct　electron　mechanism.　The　present　work　not　only　explores　high　performance　for　the　selectively　electrocatalytic　reduction　from　nitrate　to　ammonia　but　also　promote　new　inspiration　for　the　preparation　of　other　Co-based　functional　materials　for　reducing　the　production　of　nitrite.