Abstract:The new rice variety"Zhongtie 31"bred by fast-neutron irradiation has been compared with its original"Tieqiu 15"and some other types of high-yield rice varieties.The results showed that the high yield of the new variety was due to more seed-setting panicles,more spikelets per pan- icle,greater ratio of grain to stem,more nutrients transported and stored in seeds,quicker increase day matter of at late stage.However,the fer- tility of this variety was more or less affect,because the chlorophyll con- tent of leaves reduced fairly quickly at medium-late stage.If proper am- ount of fertilizer is applied at heading stage,the high-yield potentialities could be brought into full play.