The geomorphologic map of Yangtze River from Yichang to Shashi has been drawn by computer. In regarding to the outflow jamming effect from Dongting Lake a channel detention curve was established by taking the water stage at Lianhuatang station downstream as the reference parameter. It has been verified by using water balance method. When applied to flood routing for the river reach in large water years the curve obviously improves the simulated flood processes especially the result of the highest water stage. The comparison analysis shows that the calculated channel detentions of the reach are stable. Compared with the traditional methods computer technology has the advantage of accuracy and efficiency.