Abstract: Field experiments with two treatments that were normal paddy rice and aerobic rice with straw mulching were set up to explore the relationship of root growth and yield of Rice in different water condition. The result showed that: The root/shoot ratio of aerobic rice was 23.2% higher than that of normal paddy rice. The maximum deepth of rice root was 28cm for normal paddy rice and 35cm for aerobic rice. From paddy to aerobic condition the respiration intensity of rice root increased obviously during grain-filling period. In the first season the range of yield decrease of root-cutting treatments for normal paddy rice was from 15% to 23%. However, the yield of aerobic rice with 1/4 root-cut treatment increased about 20%. In the second season the yields among treatments with root-cutting for normal paddy rice were not significantly difference, but for aerobic rice the yields declined with the degree of root cut off. The yield of treatment with 3/4 root-cut in aerobic rice decreased about 20.4% and the difference was significantly. In the first season root-cutting was in disadvantage of exportating reserved assimilate but was in advantage of concurrent photoassimilate accumulation. At last the weight of spiklet of aerobic rice increased with root-cutting whereas normal paddy rice decreased. In the second season, for aerobic rice the export of reserved assimilate decreased with root-cutting, whereas the concurrent photoassimilate increased with 1/4 root cut-off. Excessive root-cutting would bring down the accumulation of concurrent photoassimilate and result in the decrease of spiklet. For normal paddy rice root-cutting did not have much effect on the reserved assimilate exporting and concurrent photoassimilate increased with 1/4 root-cut treatment, but excessive root-cutting brought down the net accumulation of concurrent photoassimilate.