Abstract: The correlations of the dry biomass and activity of root system with grain yield in raton rice in several varieties and different N application levels were studied．The results show that the grain yield of the first crop of raton rice shows significant correlation with dry matter weight(DMW )and activity of root system；the development of raton tillers depends on the remnant root system of the first crop；panicle numbers and grain yield of the second crop of raton rice show a high significant positive correlation with the activity of rot system at mature stage of the first crop and at full heading stage of the second crop，and show a parabola corelation with N applications of bud fertilizer．