A microcosmic experiment was carried out to evaluate effects of nutrients,citrate,tillage and special inocula on bioremediation of petroleum contaminated soils.Results show that indigenous microbial population,especially hydrocarbon-degrader,and petroleum removing rate increased significantly with addition of nutrients.But inoculation,addition of citrate and tillage did not show much effect on degrading rate.After 120 days of remediation,pennisetum and alfalfa were planted to study their effects on petroleum degradation,and results show that pennisetum significantly increased petroleum removal rate.In addition,denaturing gradient gel electrophoresis(DGGE)was used to study biodiversity of the bacteria in the soil after bioremediation.The p rofiles of PCR-DGGE revealed differences in microbial community structure between treatments and a higher level of bacterial diversity in treated soils than in the control as was estimated by counting the total number of bands visualized.