From observing the trough cross stratification in the outcrop of the Altyn mountain in the western Qaidam Basin, they were classified large scale, medium and small scale cross stratification according to the geometric characters; On the basis of the lithologic characters, the trough cross stratification were divided into single lithologic and multiple unit. The study of the hydrodynamics indicates that the reliable data of the paleocurrent can be collected through features of the size grading, low angle inclined bedding and the backward bedding. The geometric characters of cross stratifications reveal that the current in the early Mesozoic went along the direction from northeast to sourthwest in the northeast and went along two directions: southwesterly in the northwest part and southwesterly in the southwest. The Altun slope was subsided continuously during the middle-late Jurassic.