Abstract: In 1986,a study was initiated on the 8 or 9 year old Cunninghamia lanceolata plantations with different retained density after thinning at the Shangcun Forest Farm of the Experimental Center for Subtropical Forestry under the Chinese Academy of Forestry (CAF), which is located in Fenyi County of Jiangxi Province. Six sample plots were set up in the Chinese fir plantations with stand density of 3 000 trees·hm-2, 2 400 trees·hm-2and 1 500 trees·hm-2and with the canopy density of 0.9,0.7 and 0.6 respectively. The annual investigation has been made for 13 years on the development of undergrowth vegetation in the sample plots. The results showed that the undergrowth vegetation developed rapidly and flourished in the plantations with canopy density ≤0.7 the coverage of undergrowth vegetation had reached 80%～90%,with the total amount of undergrowth biomass of 4 or 5 t·hm-2and three storey stand structure was formed in these plantations 8 to 10 years after thinning. But,in the plantations with high density,the undergrowth vegetation started developing only when the plantation grew up to 20 years old. Therefore,reasonable thinning of the plantation can be an effective way for well development of undergrowth vegetation Generally,when the plantation with initial planting density of 2 500～3 000 trees·hm-2grows up to 10 years old,the reasonable retained stand density should be 1 500～2 000 trees·hm-2and the canopy density should be 0.6～0.7 after thinning. The results also showed that the main undergrowth plant species are fernery in Cunninghamia lanceolata plantations