In order to explore the effects of biochar with different particle sizes on soil physical properties and soil carbonpool，five biochar particle size levels were set up with potexperiment:CK(nobiochar)，T1(500～2 000 μm)，T2(250～500 μm)，T3(20～250 μm)，T4(<20 μm).The results showedthat:(1)All biochar with differentparticle sizes significantly reduced soil bulkdensity，with the largest decrease by 4.13% inT4.(2)Different particle sizesof biochar significantly increased the field water holdingcapacity(WHC)，and the increase rate wasT4>T3>T2>T1，butthe difference between biochar treatments was not significant.(3)The application of biochar significantly increased the water-stable aggregateWMD，which was the highest with T4treatment，but the difference betweenT4，T3 and T2 treatmentwas not significant.(4)The soil total organiccarbon，dissolved organic carbon and readily oxidized organic carbon in thesoil treated with biochar were significantly higher than those ofCK.The conventional biochar had significantly increased soil MBC content in the early stage of flue-cured tobaccogrowth，reduced soil MBC content in laterstage.(5)The smaller thebiochar particle size，the better the improvement of the soil carbon pool management index，and the T4 had a significantincrease in the soil carbon pool managementindex.Insummary，the smaller the biochar particle size，the better the soilbulk density，field water holding capacity and agglomerate structure improvement.At the same time，the soil organic carbon activity and carbon pool management index of small particle size biochar application are better than the conventionalparticle sizebiochar.It is more conducive to improving fertility and improving soilquality.