Abstract: Effect of applying urease inhibitor(BTPT), nitration inhibitor (EP)and growing azolla on the efficiency of urea-N has been studied by using 15N-tracing technique. The results showed that, the practice of supplying BTPT or EP increased the N utilization rate and grain yield,15N recovery rate in the treatments of BTPT,EP and BTPT+EP were 17. 4%, 17.8% and 18.0% respectively and were 3. 1%, 3. 5% and 3. 7% higher than that without inhibitor (CK). The grain yield in above three treatments were 5300, 5150 and 5450 kg/hm2, and 11.85%, 8. 7% and15. 0% higher than that CK. Growing azolla in paddy field may inhibit the volatilization of ammonium and thus decrease the urea-N loss. In the treatment of growing azolla and the azolla was incorporated into paddy field, the 15N residual rates in soil were 29. 3% and 40.1%, and were 5.1% and 15.9% higher than that in wlthout azolla,and the recovery rate of 15N were 28. 8% and 34. 7%, and 3. 3% and 9. 2% more than that CK treatment. Growing azolla has less effect on increasing the grain yield in present cropping season, however, azolla incorporated as manure the rice grain yield of present season increased by 5%.