Abstract: In order to learn the effects of different fertilization regimes on soil microbial biomass C, N, P under poplar plantations, six different treatments(NPK compound fertilizer, T1; organic fertilizer, T2; biochar, T3; NPK compound fertilizer + biochar, T4; organic fertilizer + biochar, T5; control treatment, CK)were set up under the poplar plantation of 5 years old in Dongtai Forest Centre of Jiangsu Province. The fertilization treatments were completed in June 2012, and the soil samples from different sites were collected every two months during August 2012 to June 2013. The results showed that: Five different fertilization regimes significantly improved soil microbial biomass C and N content in three different soil layers, but exerted less effect on soil microbial biomass P, only T1 treatment significantly increased soil microbial biomass P content in three different soil layers, and T4 treatment significantly increased soil microbial biomass P content in 0-10 cm soil layer compared with control treatment. T2, T4 and T5 treatments tended to reduce soil microbial biomass C/N ratio in 0-10 cm and ≥10-25 cm soil layer, but only T5 treatment significantly reduced it in 0-10 cm soil layer comparing with CK. However, T1, T2, T4 and T5 treatments significantly reduced soil microbial biomass C/N ratio in ≥25-40 cm soil layer, suggesting that the improvement effect of different fertilization regimes on supply capacity and plant availability of soil N increased with the increase of soil depth. T4 treatment performed best in increasing soil microbial biomass C, N, P of poplar plantation, at the same time, can improve supply capacity and plant availability of soil N, therefore it was the optimal fertilization regime.