Abstract: Isolated pools were used to study the dynamic changes of nutrients and biological activity in soil.The results showed that(1) long-term cropping could result in soil nutrient imbalance,reduced urease,phosphatase and sucrase activities,lowered microbial biomass nitrogen,lessened number of bacteria and fungi,and increased microbial biomass carbon;and(2) deep plowing could promote nitrogen transformation,relieve acidification,and increase organic matters in the soil,conducive to tobacco growth.Furthermore,deep plowing could significantly increase soil phosphatase and sucrase activities.It had little effect on hydrogen peroxidase activity,and a negative effect on urease.Deep plowing could increase quantity of microbial biomass carbon and nitrogen in soil,which could promote the soil nutrient transformation and enzyme activities.Thus,it appeared that deep plowing could off set the harms of long-term continuous cropping on a tobacco plantation providing a significant direction for an improvement on the agricultural practice.