In order to enhance the nitrogen removal, a subsurface wastewater inifltration system (SWIS) was improved by adding peat in deep soil as carbon source for denitriifcation process. The effects of addition of carbon source in the underpart of the SWIS on nitrogen removal at different inlfuents (with the total nitrogen (TN) concentration 40 and 80 mg L-1, respectively) were investigated by soil column simulating experiments. When the relatively light pollution inlfuent with 40 mg L-1 TN was used, the average concentrations of NO3--N and TN in eflfuents were (4.69±0.235), (6.18±0.079) mg L-1, respectively, decreased by 32 and 30.8%than the control;the NO3--N concentration of all eflfuents was below the maximum contaminant level of 10 mg L-1;as high as 92.67%of the TN removal efifciency was achieved. When relatively heavy pollution inlfuent with 80 mg L-1 TN was used, the average concentrations of NO3--N and TN in eflfuents were (10.2±0.265), (12.5±0.148) mg L-1 respectively, decreased by 20 and 21.2%than the control;the NO3--N concentration of all eflfuents met the grade III of the national quality standard for ground water of China (GB/T 14848-1993) with the values less than 20 mg L-1;the TN removal efifciency of 94.1%was achieved. In summary, adding peat in the underpart of the SWIS signiifcantly decreased TN and NO3--N concentration in eflfuents and the nitrogen removal efifciency improved signiifcantly.