Incubation experiment tested to the effect of nickel (Ni) applied on soil microbial activities and popula- tions constitution in yellow soils. The results showed that lower concentration of nickel helps the microbial activi- ties, but higher concentration or more than 100 mg/kg caused the activities to decrease. Studies suggest that soil microbial biomass carban, nitrogen and soil basal respiration decreased apparently with the increasing of concentra- tion of nickel. The number of decrease of microbial activity is lower in yello soil which is planted Hyperaccumu- lator plant than non-hyperaccumulator one. Moreover, the experiment revealed that soil microbial populations constitution have changed to some extent under stress pollution by nickel. The number of soil bacterial, acttino- mycetes and fungus decrease greatly compared with non-polluted soil samples. The soil acctinomycetes is the best sensitive for heavy mental pollution. Hyperaccumulator plant caused the lesser variety of soil microbial populations constitution and contribute to resume soil ecology.