Four varieties,indica-japonica hybrid rice Yongyou 538 and Yongyou 17,indica rice Zhongzheyou 1 and japonica rice Zhejing 88 were treated under low temperatures in different time periods of grain filling stage,to analyze endogenous hormone changes and differences in different treatments in grain filling process.The results showed that the effects of low temperatures in different time periods after flowering on grain filling showed an order of early stage > middle stage > late stage,while the difference between the effects of lower temperatures on grain filling in middle and late filling stage was not significant,and the effects of low temperatures on Yongyou 17 and Zhongzheyou 1 were higher than those on Yongyou 538 and Zhejing 88. Low temperature in early filling stage after flowering significantly slowed grain filling of Yongyou 17 and prolonged filling duration,while the effect on Yongyou 538 was not significant. Under low temperature treatments after flowering,changes in endogenous hormone contents in various varieties differed to certain degrees,IAA and ZR contents in grains of Yongyou 17 in early and middle filling stage decreased significantly,while GA3 and ABA contents were improved remarkably; and Yongyou 538 showed significantly reduced GA3 content in grains,but higher IAA and ZR contents,which were the main reason for normal filling in grains. Proper hormone regulation measures could be taken in production to improve filling of rice grains under low temperature. Four varieties, indica-japonica hybrid rice Yongyou 538 and Yongyou 17, indica rice Zhongzheyou 1 and japonica rice Zhejing 88 were treated under low filling in different time periods of grain filling stage, to analyze endogenous hormone changes and differences in different treatments in grain filling process. The results showed that the effects of low temperatures in different time periods after flowering on grain filling showed an order of early stage> middle stage> late stage, while the difference between the effects of lower temperatures on grain filling in middle and late filling stage was not significant, and the effects of low temperatures on Yongyou 17 and Zhongzheyou 1 were higher than those on Yongyou 538 and Zhejing 88. Low temperature in early filling stage after flowering significantly slowed grain filling of Yongyou 17 and prolonged filling duration, while the effect on Yongyou 538 was not significant. Under low temperature treatments after flowering, changes in endogenous hormone contents in various varieties differed to certain degrees, IAA and ZR contents in grains of Yongyou 17 in early and middle filling stages decreased significantly, while GA3 and ABA contents were improved remarkably; and Yongyou 538 showed significantly reduced GA3 content in grains, but higher IAA and ZR contents, which were the main reason for normal filling in grains. Proper hormone regulation measures could be taken in production to improve filling of rice grains under low temperature.