Abstract: The AIS data from the middle reach of the Yangtze river（Tiepu waterway to Daorenji waterway） are investigated to learn the feature of the ship domain that is the important foundation of navigation safety evaluation and navigational risk analysis. The reach is segmented. The fractal box dimension of each segment of the reach is calculated according to fractal theory and the boundary of dynamic ship domain is found by fitting processing on historical AIS data. The model of dynamic ship domain in meandering channel is set up and used to study the variation of the domain with ship length and waterway depth in different plane form. The study shows that the major axis of the domain is about 3.6 times of the ship length in the investigated reach and the ratio of major axis of domain to ship length decreases as the ship length increases. The trend of decrease is more obvious when the fractal box dimension is lower.