Abstract: The variations of yield, paniclegrain structure and the optimum application amount of nitrogen of midseason hybrid rice were studied by using the cultivars, IIyou 7 and Yuxiangyou 203, in different ecological sites, soil nutrient statuses and N application levels in 2009 Data were analyzed by using variance, correlation, regression, path and partial correlations. The results show that there are significant or highly significant differences of grain yields and paniclegrain structure between the 7 sites, 4 fertilizer application treatments and 2 combination except for the maximum tillers and productive panicle. There are highly significant correlations between spikelets per panicle, seed setting percentage, 1000\|grain weight and yield. The main goals for high yield would be increase the productive panicle and seed setting percentage, which would be achieved by increasing soil organic matter and available nitrogen content in southwest China. Multiple stepwise regression analysis shows that the optimize application amount of nitrogen of midseason hybrid rice are significantly influenced by different ecological sites and soil nutrient statuses, and the determination coefficient ranges from 09995-09999, which would be used as the scientific basis for the determination of the efficient applied N amount for full scale rice cultivation.