Ammonia is an important chemical raw material and a new energy storage material. However, Its traditional manufacture process consumes a great amount of energy and emits much greenhouse gas CO2. In order to make the artificial ammonia production environmentally friendly, electrocatalytic nitrogen reduction reaction (NRR) has become one of the most promising technical methods. Since there is still no dramatic breakthrough in NH3 yield rate and Faraday efficiency, it becomes urgent to explore new catalytic materials. As far as both cost control and electrocatalytic performances are concerned, transition metal nanomaterial catalysts are occupying an increasing position in today’s research and development work of NRR. Focusing on transition metal nanomaterials, starting from the NRR mechanism including dissociative mechanism, associative pathway and the enzymatic mechanism, this article summarizes the current NRR performances of transition metal oxides, transition metal nitrides, transition metal phosphides, transition metal carbides, transition metal borides, transition metal sulfides, the composites of above compounds composites, together with relevant density functional theory (DFT) clues. What’s more, a summary of strategies that are conducive to improving the NH3 yield rate and Faraday efficiency is given, involving the adjustment of crystal facet, size and morphology engineering, vacancy engineering, heteroatom doping, and strain engineering. In all, by constantly improving NH3 yield and Faraday efficiency, transition metal nanomaterials are continuously developing in the field of NRR, and providing strong support for the industrialization of ammonia production of NRR in the future.