In order to study the effects of cultivating ginseng in farmland on soil microbial community structures,active microbial mass and community structure in rhizosphere of ginseng of 1,2,3,4 and 5 years old were determined by phosphor lipid fatty acid（PLFA）.The results showed the microorganisms containing the PLFA of i15∶0,a15∶0,16∶1ω9c and 16∶0 were dominance in microbial community in farmland root zone soil cultivating ginseng.Bacterial biomass and total biomass were decreased significantly,and total biomass was more declined at 2 years old.Fungal biomass were enhanced significantly and raised by 10 times,while actinomycete biomass increased slightly.In the community structure,fungi ratio in total biomass were enhanced compared with the control,which was key characters of soil microbial community structure in farmland cultivated ginseng.