Abstract: In order to clarify the influence of fired soil on the quality of tobacco seedlings,the floating seedling breeding method was adopted to study different amounts of fired soil seedling substrates on chlorophyll,root architecture,root activity and nitrate reductase activity of tobacco seedlings.The results showed that,the chlorophyll,total root length,root surface area,root mean diameter,root volume and root activity increased at first and then decreased,and reached peak under 50% fired soil with 50% conventional seedling substrates treatment;The root nitrate reductase activity increased with the increase of the amount of fired soil;When the proportion of fired soil was within 50%,the amount of fired soil was positively correlated with total root length and root surface area at the 0.01 level,and was positively correlated with total root volume at the 0.05 level.It was concluded that 50% fired soil together with 50% conventional seedling substrate was the best for the development of tobacco seedlings.