High nitrous oxide (N2O) emissions during freeze-thawing period (FTP) have been observed in many different ecosystems.However,the knowledge about the dynamic of soil N2O emissions and its main driving mechanism during the freeze-thawing processes in grassland ecosystem is still limited.An in-situ experiment was conducted during the FTP on the sites with 0 and 15％ surplus of the average rainfall and two levels of N addition (0,10 g N/(m2·year)) during growing season (marked as W0N0,W15N0,W0N10,W15N10,respectively) to explore the effects of water and N background on soil N2O emissions during FTPs and the relationship between soil N2O emissions and environmental factors.The results indicated that water and N treatments conducted during growing season did not show significant effect on the N2O effiuxes of FTP,but the soil mineral N contents of W0N10 treatment were significantly higher than those of W0N0,W15N0,W15N10 treatments (p ＜ 0.05).The soil PLFA concentrations of microbial groups monitored during 2015 spring freeze-thawing period (2015S-FTP) were lower than those during winter freeze-thawing period of 2014 (2014W-FTP),while cumulative soil N2O emissions of 2015S-FTP were higher than those of 2014W-FTP.The correlations between soil N2O effluxes and most of the measured environmental factors were insignificant,multiple stepwise regression analysis indicated that the soil temperature,soil NH4+-N content and air temperature were the major environmental factors which significantly influenced the N2O effluxes during 2014W-FTP,and air temperature and soil water content were the significant influencing factors during 2015S-FTP.