Abstract: Research on effect of undergrowth in Chinese fir plantation on the soil properties in the 5～15 cm layer was conducted in the Dagang Mountain,Shan Xia Forest Farm,Jiangxi Province. The results show that the amount of bacteria,actinomycetes,fungi,bacillus spp in bacteria,grey hyphae in actinomycetes and trichoderma pers,ex Fr,Aspergillus in fungi increase with the increase of the undergrowth coverage, Soil enzyme activity,and carbon content of various composition of humus in the 16 and 18 site index plots also increase in positive proportion with the increase of the undergrowth,however,in the 14 site index plot,the results turn out contrary to the former. Amount of soil organic matter,available N and total exchangeable base in the 16 site index plot increase with the increase of the under-growth coverage. Amount of soil organic matter,total N,available N,P,K and Ca2+,Mg2+ cotent in the 18 site index plot also increase with the increase of the undergrowth coverage.