Geomorphologic and geological characteristics of the river throats in the middle Yangtze River between Wuhan and Jiujiang and blocking effects of the river throats are studied. In this paper, the Tianjiazhen river throat serves as the case in the research on the blocking effects of river throat to the flood runoff. Hydrological data obtained from the field investigation in 2003, together with the historical hydrological data are applied in the discharge effects of the river blocks. Research results indicate that, under the influence of the conformation activities of the Huaiyang shield, the river channel in the middle Yangtze River moved southward. The south bank of the study river channel is characterized by mountain and north bank is characterized by alluvium plain. Most river blocks are composed of the single projecting rock, which make the river channel static and the river section narrow, acting as the obstacle preventing the discharge of the flood from the middle Yangtze River. Watertime materials indicate that the time for transformation from Hankou to Wuxue is about 24 hours if the runoff is below 60 000m³/s, the time will be 72 hours if the runoff reaches 76 100m³/s in Hankou and 48 hours for the runoff of 72 300 m³/s in Hankou. Water level shape for the peak flood flow is flat and wide and relatively pointed and narrow when the water level is low, indicating that the peak flow will spend more time than the lower water level (<18m in Wuxue, Huanghai altitude level), demonstrating the blocking function of the river throats in the middle Yangtze River. Research results demonstrate the advantage of widening of the river channel in discharge of the flood from the middle Yangtze River, putting forward the flood mitigation measurements. The further research will be: the influence of the widening of the river blocks on the river channel; influences of the the widening of the river throat on flood controlling activities of Jiangxi and Anhui Province; economic comparison between the flood controlling effects of the widening and the engineering expenditure.