The problem of nitrate accumulation and leaching in greenhouse soil has been drawn increasing attention.A field plot experiment was conducted to study the effect of biochar on dynamic changes of NO-3-N in greenhouse soil.The results showed that the biochar improved the soil NO-3-N content in the early stage,but significantly reduced the accumulation of nitrate in surface and profile soil of greenhouse in the late stage.For example,T2,T3,T4 compared with T1,surface soil NO-3-N contents were reduced by 11.71%,16.08% and 24.83%,the accumulation of NO-3-N in soil profile were reduced by 11.63%,17.51% and 25.38%,respectively,in the late stage of tomato.There was obvious seasonal change of nitrate content in greenhouse soil.The application of biochar reduced greenhouse soil nitrate annual variations.The greater the amount of use,the effect was more obvious.For example,annual variations of T2,T3,T4 compared with T1 were reduced by 12.35%,13.72% and 25.99%,respectively.The application of biochar also reduced the nitrate content of vegetables,and the greater the amount,the more obvious effects.The low amount of biochar had little effect on vegetable yields or improved the yields,but with increasing use dose,the yields tended to decline.Therefore,the application amount of biochar should not be too high in greenhouse soil.