Nitrous oxide (N₂O) is a long-lived greenhouse gas that can destroy stratospheric ozone.Agricultural soil is the largest contributor to anthropogenic N₂O emissions.It is thus urgent to reduce N₂O emissions from agricultural soil.Biochar is a carbon material produced by pyrolysis of biomass at low temperature and limited oxygen with rich pore structures.Biochar is one of the important means to reduce greenhouse N₂O emissions,but there are few systematic reports on its effect and mechanism.We describe the effects of biochar on N₂O emissions from soil.We then discuss the possible mechanisms of biochar on soil N₂O emissions.From a biological point of view,the"liming effect"of biochar could increase soil pH and change soil microbial processes to promote the reduction of N₂O to N₂,and also act as an "electron shuttle" in this process.In addition,biochar could increase the population of denitrification bacteria containing nosZ gene to promote the reduction of N₂O to N₂.When soil N₂O was mainly generated through nitrification,the addition of biochar could increase the abundance of ammonia-oxidizing bacteria harboring amoA gene in soil,which led to the increase of soil N₂O emissions.From an abiotic point of view,the adsorption of N₂O on the surface of biochar could reduce the release of N₂O emission from soil,and then the surface C C may react with N₂O to consume it.The effects of biochar amendments on N₂O emissions depend on the characteristics of biochar (raw materials,pyrolysis conditions,C/N ratio,application rate,and aging degree),nitrogen application rate,and soil physico-chemical properties.Finally,we summarize and put forward further prospect on biochar in reducing N₂O emissions from soil.This review will provide an important technical reference for mitigation of N₂O emissions from agricultural soil as well as agricultural carbon neutrality in the future.