In order to evaluate the effects of carbon-nitrogen ratio (CNR) on nitrous oxide (N2O) emission and quantify N2O spatial distribution in subsurface wastewater infiltration system (SWIS), layered sampling method was introduced. Results showed that low N2O emission rate (1.43 mg/m(2).h) and conversion rate (0.1% accounting for influent TN) were obtained when CNR increased up to as high as 10. The highest N2O emission (3.14 mg/m(2).h) was observed at CNR of 6. Instead, independent of CNR variations, 0-75 cm was the main contributor for N2O emission. The results indicated that layered sampling method is necessary in revealing N2O spatial distribution in soil layers. Carbon source availability and nitrogen load and their ratio (i.e. CNR) determined N2O emission rate. CNR of medium level leads to an increase in N2O emission rate.